No Verification Email Is Sent when New User is Registering

I've installed your plugin as it is recommended by MemberPress for email verification of new users. I've followed the instructions in the long below, but when registering a new user, no email is sent for verification. I've also tried logging in with that same user and resending the verification email from the login page. However it throws an error when trying that. What am I doing wrong?

How to require Email Verification on registration

Sending Email Verification...

Sorry! there was an error.