diff --git a/.changeset/tired-parents-like.md b/.changeset/tired-parents-like.md
new file mode 100644
index 0000000000..11036e6e2a
--- /dev/null
+++ b/.changeset/tired-parents-like.md
@@ -0,0 +1,6 @@
+---
+"@medusajs/fulfillment": minor
+"@medusajs/types": minor
+---
+
+fix(fulfillment, types): make relationship between SO and SO type M:1
diff --git a/packages/core/types/src/fulfillment/mutations/shipping-option.ts b/packages/core/types/src/fulfillment/mutations/shipping-option.ts
index ad878ca45c..3d694308f8 100644
--- a/packages/core/types/src/fulfillment/mutations/shipping-option.ts
+++ b/packages/core/types/src/fulfillment/mutations/shipping-option.ts
@@ -83,11 +83,23 @@ export interface UpdateShippingOptionDTO {
    */
   provider_id?: string
 
+  /**
+   * The ID of the shipping option type.
+   */
+  shipping_option_type_id?: string
+
+  /**
+   * The ID of the type of shipping option.
+   * Column doesn't exist on the entity -> normalized to `shipping_option_type_id`
+   */
+  type_id?: string
+
   /**
    * The shipping option type associated with the shipping option.
    */
   type?:
-    | CreateShippingOptionTypeDTO | string
+    | CreateShippingOptionTypeDTO
+    | string
     | {
         /**
          * The ID of the shipping option type.
@@ -133,35 +145,35 @@ type CalculateShippingItems = {
 
 export type CalculatedRMAShippingContext =
   | {
-    /**
-     * The ID of the return.
-     */ 
-    return_id: string
-    /**
-     * The details of the return's items.
-     */
-    return_items: CalculateShippingItems[]
-  }
+      /**
+       * The ID of the return.
+       */
+      return_id: string
+      /**
+       * The details of the return's items.
+       */
+      return_items: CalculateShippingItems[]
+    }
   | {
-    /**
-     * The ID of the exchange.
-     */
-    exchange_id: string
-    /**
-     * The details of the exchange's items.
-     */ 
-    exchange_items: CalculateShippingItems[]
-  }
+      /**
+       * The ID of the exchange.
+       */
+      exchange_id: string
+      /**
+       * The details of the exchange's items.
+       */
+      exchange_items: CalculateShippingItems[]
+    }
   | {
-    /**
-     * The ID of the claim.
-     */ 
-    claim_id: string
-    /**
-     * The details of the claim's items.
-     */
-    claim_items: CalculateShippingItems[]
-  }
+      /**
+       * The ID of the claim.
+       */
+      claim_id: string
+      /**
+       * The details of the claim's items.
+       */
+      claim_items: CalculateShippingItems[]
+    }
 
 /**
  * The data needed for the associated fulfillment provider to calculate the price of a shipping option.
diff --git a/packages/modules/fulfillment/src/migrations/.snapshot-medusa-fulfillment.json b/packages/modules/fulfillment/src/migrations/.snapshot-medusa-fulfillment.json
index eb7e7fec8f..4b306733de 100644
--- a/packages/modules/fulfillment/src/migrations/.snapshot-medusa-fulfillment.json
+++ b/packages/modules/fulfillment/src/migrations/.snapshot-medusa-fulfillment.json
@@ -157,7 +157,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_fulfillment_address_deleted_at\" ON \"fulfillment_address\" (deleted_at) WHERE deleted_at IS NULL"
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_fulfillment_address_deleted_at\" ON \"fulfillment_address\" (\"deleted_at\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "fulfillment_address_pkey",
@@ -238,7 +238,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_fulfillment_provider_deleted_at\" ON \"fulfillment_provider\" (deleted_at) WHERE deleted_at IS NULL"
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_fulfillment_provider_deleted_at\" ON \"fulfillment_provider\" (\"deleted_at\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "fulfillment_provider_pkey",
@@ -336,7 +336,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_fulfillment_set_deleted_at\" ON \"fulfillment_set\" (deleted_at) WHERE deleted_at IS NULL"
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_fulfillment_set_deleted_at\" ON \"fulfillment_set\" (\"deleted_at\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "IDX_fulfillment_set_name_unique",
@@ -345,7 +345,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE UNIQUE INDEX IF NOT EXISTS \"IDX_fulfillment_set_name_unique\" ON \"fulfillment_set\" (name) WHERE deleted_at IS NULL"
+          "expression": "CREATE UNIQUE INDEX IF NOT EXISTS \"IDX_fulfillment_set_name_unique\" ON \"fulfillment_set\" (\"name\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "fulfillment_set_pkey",
@@ -443,7 +443,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_service_zone_fulfillment_set_id\" ON \"service_zone\" (fulfillment_set_id) WHERE deleted_at IS NULL"
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_service_zone_fulfillment_set_id\" ON \"service_zone\" (\"fulfillment_set_id\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "IDX_service_zone_deleted_at",
@@ -452,7 +452,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_service_zone_deleted_at\" ON \"service_zone\" (deleted_at) WHERE deleted_at IS NULL"
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_service_zone_deleted_at\" ON \"service_zone\" (\"deleted_at\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "IDX_service_zone_name_unique",
@@ -461,7 +461,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE UNIQUE INDEX IF NOT EXISTS \"IDX_service_zone_name_unique\" ON \"service_zone\" (name) WHERE deleted_at IS NULL"
+          "expression": "CREATE UNIQUE INDEX IF NOT EXISTS \"IDX_service_zone_name_unique\" ON \"service_zone\" (\"name\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "service_zone_pkey",
@@ -616,7 +616,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_geo_zone_service_zone_id\" ON \"geo_zone\" (service_zone_id) WHERE deleted_at IS NULL"
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_geo_zone_service_zone_id\" ON \"geo_zone\" (\"service_zone_id\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "IDX_geo_zone_deleted_at",
@@ -625,7 +625,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_geo_zone_deleted_at\" ON \"geo_zone\" (deleted_at) WHERE deleted_at IS NULL"
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_geo_zone_deleted_at\" ON \"geo_zone\" (\"deleted_at\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "IDX_geo_zone_country_code",
@@ -634,7 +634,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_geo_zone_country_code\" ON \"geo_zone\" (country_code) WHERE deleted_at IS NULL"
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_geo_zone_country_code\" ON \"geo_zone\" (\"country_code\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "IDX_geo_zone_province_code",
@@ -643,7 +643,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_geo_zone_province_code\" ON \"geo_zone\" (province_code) WHERE deleted_at IS NULL"
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_geo_zone_province_code\" ON \"geo_zone\" (\"province_code\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "IDX_geo_zone_city",
@@ -652,7 +652,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_geo_zone_city\" ON \"geo_zone\" (city) WHERE deleted_at IS NULL"
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_geo_zone_city\" ON \"geo_zone\" (\"city\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "geo_zone_pkey",
@@ -764,7 +764,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_shipping_option_type_deleted_at\" ON \"shipping_option_type\" (deleted_at) WHERE deleted_at IS NULL"
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_shipping_option_type_deleted_at\" ON \"shipping_option_type\" (\"deleted_at\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "shipping_option_type_pkey",
@@ -862,7 +862,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_shipping_profile_deleted_at\" ON \"shipping_profile\" (deleted_at) WHERE deleted_at IS NULL"
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_shipping_profile_deleted_at\" ON \"shipping_profile\" (\"deleted_at\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "IDX_shipping_profile_name_unique",
@@ -871,7 +871,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE UNIQUE INDEX IF NOT EXISTS \"IDX_shipping_profile_name_unique\" ON \"shipping_profile\" (name) WHERE deleted_at IS NULL"
+          "expression": "CREATE UNIQUE INDEX IF NOT EXISTS \"IDX_shipping_profile_name_unique\" ON \"shipping_profile\" (\"name\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "shipping_profile_pkey",
@@ -1019,7 +1019,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_shipping_option_service_zone_id\" ON \"shipping_option\" (service_zone_id) WHERE deleted_at IS NULL"
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_shipping_option_service_zone_id\" ON \"shipping_option\" (\"service_zone_id\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "IDX_shipping_option_shipping_profile_id",
@@ -1028,7 +1028,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_shipping_option_shipping_profile_id\" ON \"shipping_option\" (shipping_profile_id) WHERE deleted_at IS NULL"
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_shipping_option_shipping_profile_id\" ON \"shipping_option\" (\"shipping_profile_id\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "IDX_shipping_option_provider_id",
@@ -1037,7 +1037,16 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_shipping_option_provider_id\" ON \"shipping_option\" (provider_id) WHERE deleted_at IS NULL"
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_shipping_option_provider_id\" ON \"shipping_option\" (\"provider_id\") WHERE deleted_at IS NULL"
+        },
+        {
+          "keyName": "IDX_shipping_option_shipping_option_type_id",
+          "columnNames": [],
+          "composite": false,
+          "constraint": false,
+          "primary": false,
+          "unique": false,
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_shipping_option_shipping_option_type_id\" ON \"shipping_option\" (\"shipping_option_type_id\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "IDX_shipping_option_deleted_at",
@@ -1046,7 +1055,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_shipping_option_deleted_at\" ON \"shipping_option\" (deleted_at) WHERE deleted_at IS NULL"
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_shipping_option_deleted_at\" ON \"shipping_option\" (\"deleted_at\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "shipping_option_pkey",
@@ -1215,7 +1224,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_shipping_option_rule_shipping_option_id\" ON \"shipping_option_rule\" (shipping_option_id) WHERE deleted_at IS NULL"
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_shipping_option_rule_shipping_option_id\" ON \"shipping_option_rule\" (\"shipping_option_id\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "IDX_shipping_option_rule_deleted_at",
@@ -1224,7 +1233,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_shipping_option_rule_deleted_at\" ON \"shipping_option_rule\" (deleted_at) WHERE deleted_at IS NULL"
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_shipping_option_rule_deleted_at\" ON \"shipping_option_rule\" (\"deleted_at\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "shipping_option_rule_pkey",
@@ -1431,7 +1440,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_fulfillment_shipping_option_id\" ON \"fulfillment\" (shipping_option_id) WHERE deleted_at IS NULL"
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_fulfillment_shipping_option_id\" ON \"fulfillment\" (\"shipping_option_id\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "IDX_fulfillment_deleted_at",
@@ -1440,7 +1449,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_fulfillment_deleted_at\" ON \"fulfillment\" (deleted_at) WHERE deleted_at IS NULL"
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_fulfillment_deleted_at\" ON \"fulfillment\" (\"deleted_at\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "IDX_fulfillment_location_id",
@@ -1449,7 +1458,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_fulfillment_location_id\" ON \"fulfillment\" (location_id) WHERE deleted_at IS NULL"
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_fulfillment_location_id\" ON \"fulfillment\" (\"location_id\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "fulfillment_pkey",
@@ -1596,7 +1605,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_fulfillment_label_fulfillment_id\" ON \"fulfillment_label\" (fulfillment_id) WHERE deleted_at IS NULL"
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_fulfillment_label_fulfillment_id\" ON \"fulfillment_label\" (\"fulfillment_id\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "IDX_fulfillment_label_deleted_at",
@@ -1605,7 +1614,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_fulfillment_label_deleted_at\" ON \"fulfillment_label\" (deleted_at) WHERE deleted_at IS NULL"
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_fulfillment_label_deleted_at\" ON \"fulfillment_label\" (\"deleted_at\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "fulfillment_label_pkey",
@@ -1762,7 +1771,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_fulfillment_item_fulfillment_id\" ON \"fulfillment_item\" (fulfillment_id) WHERE deleted_at IS NULL"
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_fulfillment_item_fulfillment_id\" ON \"fulfillment_item\" (\"fulfillment_id\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "IDX_fulfillment_item_deleted_at",
@@ -1771,7 +1780,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_fulfillment_item_deleted_at\" ON \"fulfillment_item\" (deleted_at) WHERE deleted_at IS NULL"
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_fulfillment_item_deleted_at\" ON \"fulfillment_item\" (\"deleted_at\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "IDX_fulfillment_item_inventory_item_id",
@@ -1780,7 +1789,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_fulfillment_item_inventory_item_id\" ON \"fulfillment_item\" (inventory_item_id) WHERE deleted_at IS NULL"
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_fulfillment_item_inventory_item_id\" ON \"fulfillment_item\" (\"inventory_item_id\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "IDX_fulfillment_item_line_item_id",
@@ -1789,7 +1798,7 @@
           "constraint": false,
           "primary": false,
           "unique": false,
-          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_fulfillment_item_line_item_id\" ON \"fulfillment_item\" (line_item_id) WHERE deleted_at IS NULL"
+          "expression": "CREATE INDEX IF NOT EXISTS \"IDX_fulfillment_item_line_item_id\" ON \"fulfillment_item\" (\"line_item_id\") WHERE deleted_at IS NULL"
         },
         {
           "keyName": "fulfillment_item_pkey",
diff --git a/packages/modules/fulfillment/src/migrations/Migration20251114133146.ts b/packages/modules/fulfillment/src/migrations/Migration20251114133146.ts
new file mode 100644
index 0000000000..0fa7fe5767
--- /dev/null
+++ b/packages/modules/fulfillment/src/migrations/Migration20251114133146.ts
@@ -0,0 +1,13 @@
+import { Migration } from '@mikro-orm/migrations';
+
+export class Migration20251114133146 extends Migration {
+
+  override async up(): Promise<void> {
+    this.addSql(`CREATE INDEX IF NOT EXISTS "IDX_shipping_option_shipping_option_type_id" ON "shipping_option" ("shipping_option_type_id") WHERE deleted_at IS NULL;`);
+  }
+
+  override async down(): Promise<void> {
+    this.addSql(`drop index if exists "IDX_shipping_option_shipping_option_type_id";`);
+  }
+
+}
diff --git a/packages/modules/fulfillment/src/models/shipping-option-type.ts b/packages/modules/fulfillment/src/models/shipping-option-type.ts
index 065a8b10ed..31c74b3bbb 100644
--- a/packages/modules/fulfillment/src/models/shipping-option-type.ts
+++ b/packages/modules/fulfillment/src/models/shipping-option-type.ts
@@ -7,7 +7,7 @@ export const ShippingOptionType = model.define("shipping_option_type", {
   label: model.text().searchable(),
   description: model.text().searchable().nullable(),
   code: model.text().searchable(),
-  shipping_option: model.hasOne(() => ShippingOption, {
+  shipping_options: model.hasMany(() => ShippingOption, {
     mappedBy: "type",
   }),
 })
diff --git a/packages/modules/fulfillment/src/models/shipping-option.ts b/packages/modules/fulfillment/src/models/shipping-option.ts
index 9a1ee4ff3b..a43c6227f7 100644
--- a/packages/modules/fulfillment/src/models/shipping-option.ts
+++ b/packages/modules/fulfillment/src/models/shipping-option.ts
@@ -25,10 +25,10 @@ export const ShippingOption = model
       })
       .nullable(),
     provider: model.belongsTo(() => FulfillmentProvider).nullable(),
-    type: model.hasOne(() => ShippingOptionType, {
+    type: model.belongsTo(() => ShippingOptionType, {
       foreignKey: true,
       foreignKeyName: "shipping_option_type_id",
-      mappedBy: undefined,
+      mappedBy: "shipping_options",
     }),
     rules: model.hasMany(() => ShippingOptionRule, {
       mappedBy: "shipping_option",
diff --git a/packages/modules/fulfillment/src/services/fulfillment-module-service.ts b/packages/modules/fulfillment/src/services/fulfillment-module-service.ts
index 2de8932ae0..124fceaa72 100644
--- a/packages/modules/fulfillment/src/services/fulfillment-module-service.ts
+++ b/packages/modules/fulfillment/src/services/fulfillment-module-service.ts
@@ -35,7 +35,6 @@ import {
   ModulesSdkUtils,
   promiseAll,
 } from "@medusajs/framework/utils"
-import { isObject } from "@medusajs/utils"
 import {
   Fulfillment,
   FulfillmentProvider,
@@ -1282,6 +1281,7 @@ export default class FulfillmentModuleService
       },
       sharedContext
     )
+
     const existingShippingOptions = new Map(
       shippingOptions.map((s) => [s.id, s])
     )
@@ -1295,15 +1295,15 @@ export default class FulfillmentModuleService
     const updatedRuleIds: string[] = []
     const existingRuleIds: string[] = []
 
-    const optionTypeDeletedIds: string[] = []
-
     dataArray.forEach((shippingOption) => {
       const existingShippingOption = existingShippingOptions.get(
         shippingOption.id
       )! // Guaranteed to exist since the validation above have been performed
 
-      if (isObject(shippingOption.type) && !("id" in shippingOption.type)) {
-        optionTypeDeletedIds.push(existingShippingOption.type.id)
+      // `type_id` doesn't exist on the entity/table, `type_id` argument is mapped to `shipping_option_type_id`
+      if (shippingOption.type_id) {
+        shippingOption.shipping_option_type_id = shippingOption.type_id
+        delete shippingOption.type_id
       }
 
       if (!shippingOption.rules) {