Please go to Amazon Developer Center page https://sellercentral.amazon.com/gp/homepage.html in the Register Your Application, create a new client ID, and in the line 23 set the client_id to Cliente ID and client_secret with Client Secret. The callback URL must be https://erp.leaf.com.my/webmail/modules/OAuthIntegratorWebclient/Classes/OAuthClient/login_with_amazon.php but make sure the domain is valid and can be resolved by a public DNS.