Hey @Stephanie Atse45! We have a guide on how to set up our integration with Thrive here92. Just to confirm, are those the instructions you were following? :)
As for the deliverability issue, could you please check that your account's sending address is an @customdomain email address? We have more info on that here58.
If you're still having trouble after that, I'd recommend reaching out to our team at help@convertkit.com38 (or via the in-app messenger in your account) with a description of this issue, including screenshots if possible of how you set it up, as well as the email address(es) you tested it out with. One of our Product Specialists will be able to help troubleshoot further!