Hello Simon

If the Appointment Approved notification is enabled in Notifications section, they should be sent.

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.

Hello Benjamin

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. When using Gmail, please verify 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 but please make sure to enable the PRIVATE response as this ticket is public