It could've been that permissions granted to our MWS access has accidentally been removed from your Amazon Seller Central.
Your Amazon account may have been suspended.
It is also possible that you account has simply expired and needs to be updated.
To allow SellerChamp have access to your Amazon account, please make sure you follow the steps below:
Login to your Amazon Seller Central and check here Amazon MWS Permissions Manager to make sure SellerChamp still has developer access to your account.V
Verify that your Amazon Seller ID and Amazon MWS token match on SellerChamp. Seller ID would be here