I have a new problem though. Registering a new user fails at ValidateUser. What am I missing here?

Issue has been fixed in latest commit in the github repo

I commented on the commit. The corresponding cshtml files need the same fix. Thanks again!

For future developers working on integrating an API for the email service: MimeMessage.From and mimeMessage.To contain both the username and email. If your emails are getting blocked due to a syntax error, make sure the HTTP request has the email address as: {UserName username@gmail.com} and not {Username }

For me, this error was from mapping MimeMessages to a SendGrid email request, and it was difficult to track down!