fix(medusa-plugin-brightpearl): External ref split (#4295)

* order should be first part of external_ref

* add changeset

---------

Co-authored-by: Oliver Windall Juhl <59018053+olivermrbl@users.noreply.github.com>

.changeset/weak-waves-watch.md

@@ -0,0 +1,5 @@
+---
+"medusa-plugin-brightpearl": patch
+---
+
+fix(brightpearl): split externalRef to get product id

packages/medusa-plugin-brightpearl/src/services/brightpearl.js

@@ -1705,7 +1705,7 @@ class BrightpearlService extends BaseService {
       const { fulfillments: existingFulfillments, sales_channel } =
         await this.orderService_
           .withTransaction(transactionManager)
-          .retrieve(order.externalRef, {
+          .retrieve(order.externalRef.split(".")[0], {
             relations: ["fulfillments", "sales_channel"],
           })