When I click pay with or login by amazon following message showing?

We’re sorry!
An error occurred when we tried to process your request. Rest assured, we’re already working on the problem and expect to resolve it shortly.

Error Summary
400 Bad Request
The redirect URI you provided has not been whitelisted for your application. Please add your redirect URI in the ‘Allowed Return URLs’ section under ‘Web Settings’ on the Amazon Seller Central App Console for Login with Amazon.
Request Details
redirect_uri=https%3A%2F%2Ffasonwear.com %2Fen%2Fmodule%2Famzpayments%2Fprocess_login

Thank you for your post. Unfortunately, I would not be able to fully assist with the error you are receiving. Please contact the Seller Support team from your Pay with Amazon account for further assistance with this matter.