This error will be shown if you Chargebee site name has not been configured in the “Allowed login domains” under Amazon payments, during the setup process. Screenshot of the page for reference:

 

You need to enter your Chargebee domain URL here to connect with your Amazon Buyer Account. During testing, configure your Chargebee TEST domain name and later on you can change this in your Amazon account console. You should also include your Chargebee customer portal domain name if you've enabled the customer portal through the Amazon account console.

More information on configuring Amazon Payments with Chargebee is here.