Sign-up procedure fails on confirmation email sending

[quapka]

Hi folks,
I wanted to test your application, but the sign-up feature is not working as expected. After attempting to register with some name and a valid e-mail the following error is displayed:

Error: Error sending confirmation email: {
"errors":[
"Failed to send email: 550 5.7.1 This sender is not authorized to send from multifactor.com. See https://bit.ly/domain-lockdown. cfid=mfkdf-application-demo.pages.dev"]
} 

The underlying POST request to https://demo.mfkdf.com/api/verify?email=<email>&name=<name> fails with 500 HTTP code.