Email notifications not working correctly

Hello, all. I am having an issue with the Appointments+ plugin not sending the confirmation email to the service provider and the admin. It was working correctly, but about a month ago (maybe more) it has stopped sending them. The admin is getting the email from PayPal when the deposit is sent, but no email comes to them from Appointments+.

I saw another thread opened on this issue, but unfortunately has not yet been resolved. Any ideas how I can get this working? Thanks in advance for any help!