Bug regarding email verification?

I have purchased and using the Appointments+ plugin to create a booking form for our office use.
I am testing the booking form now but not receiving any email notification for both the service provider and the customer even when i have the option "Send Confirmation email" set to yes.

Instead of the default wp_mail, i am a using a plugin from sendgrid which replaces that and uses their own api to send mail instead (sendgrid.com)
This is confirmed to be working in the test of sendgrid plugin and in other plugins such as contact form 7.

is there a way to make use of this email, or must i use wp_mail?

Attached is screenshot of the settings in appointments+

Thank you in advance.