TABLE OF CONTENTS
Overview.
Connection issues between Omnivore and Amazon can sometimes affect order flow from Amazon to your eCommerce Store. Specifically in this case the issue and resolution actually sits within Amazon itself.
The error in Omnivore that flags this issue is - 'Cannot connect to your Amazon account, the error is: Access to Orders.ListOrders is denied'.
This error will show if you attempt a test connection from Settings, Amazon, General, Check Connection.
Fix
The resolution for this is to log into your Seller Central Account in Amazon and follow these steps to fix the connection between Amazon and Omnivore.
Navigate to Apps & Services > Manage My Apps. You will note that the Omnivore application has been disabled due to authorisation expiry.
For Omnivore to continue making calls on the your behalf, you must renew/enable the application which will then trigger creation of an MWS auth token. 
The auth token, alongside your Merchant Token, are the two identifiers Omnivore uses to make calls on your behalf – as per the registration and authorisation workflow. Please take note of the FAQ's below.
Please enable the Omnivore application and provide identifiers are required.
More Information.
We also recommend referring to these FAQ's.
