Hello Adrian

Thank you for your purchase, and sorry to hear you're having issues.

Issue with email notifications could be caused by several reasons:

1. Your hosting provider is blocking all 3rd party settings, and only allowing their SMTP (or other) settings. 

2. Your website has PHP version less than 7 

3. The credentials are not correct 

4. There's something else blocking the notifications from being sent.

5. For Gmail - have you enabled "Allow less secure apps" in your Google Account?

Please check these points, and let me know if you were able to resolve the issue. If you're not able to resolve the issue, please provide me a temporary WP-admin login for your site where this happens, so we could log in and take a look ‘from the inside’ as that’s the most efficient way to see and resolve the issue. We do not interfere with any data or anything else except for the plugin (in case that’s a production version of the site), and of course we do not provide login data to third party. 

You can write credentials here just check Private Reply so nobody can see them except us.