docs: add troubleshooting for middlewares (#13764)

www/apps/book/public/llms-full.txt

@@ -1384,6 +1384,12 @@ This returns the created brand in the response:
 }
 ```
 
+### Troubleshooting
+
+#### Returned Empty Array
+
+If you sent a request to the API route and received an empty array in the response, make sure you've correctly created the middleware at `src/api/middlewares.ts` (with correct spelling). This is a common mistake that can lead to the middleware not being applied, resulting in unexpected behavior.
+
 ***
 
 ## Summary
@@ -8180,6 +8186,10 @@ npm run dev
 Received a request!
 ```
 
+### Troubleshooting
+
+If the middleware didn't run, make sure you've correctly created the middleware at `src/api/middlewares.ts` (with correct spelling). This is a common mistake that can lead to the middleware not being applied, resulting in unexpected behavior.
+
 ***
 
 ## When to Use Middlewares