Amazon Integration - Error: Operation failed - Access to the resource Unauthorized in Production: (XXXXXXX;XXXXXX) is denied.

After setting up Amazon integration you receive an error message

System.Exception: Server was unable to process request. ---> RequestInventoryReport: Operation failed - Access to the resource Unauthorized in Production: (XXXXXXXXXXXXXXXXX;XXXXXXXXXXX) is denied.

Reason:

This is due to invalid Merchant Id and MarketPlace id for the seller.

Resolution:

Open your browser
Go to Amazon Seller central and Sign Out
In Linnworks Go to Settings > Channels > select Amazon Config
Click Test
It will prompt with an error and ask you to proceed to autorization page on Amazon
Sign in to Amazon in the webbrowser
Enter the Application Name and (our) Developer Id
Get your Merchant Id and MarketPlace Id and paste it into Config window