How to get Newsletter to communicate with a sendy list?

Hi all. I’m trying to use the newsletter plugin with an existing sendy mailing list. It’s a simple email form and GDPR checkbox. I’m not sure how to sync with the existing sendy list though. I have the url and I can get the list id…just not sure how to link it all up in WordPress. Any help appreciated. I just want a simple acknowledgement that the user has been added, no redirect.