How to register domain on my website on google APIs? throws me this error : domain must be added to the autorized domain list before submitting

I want to receive emails from a contact form on my site!
Does anyone know how I can solve this problem
I don’t know how to register a domain on Gmail API
throws me this error like in the picture
I try to do this via the SMTP post plugin and follow his guide to do it
I did the same through the same plugin to send a message from the contact form on the Wordpress site that is on the localhost
but I can’t from a live hosted site