How can I log in using my Hide My Email without "Sign in with Apple" option?

I signed up to Myq app using the hide my email feature. However, if I try to go their website and log in there. There's no option to login with Apple id. In this case, even if I copy the random email copied by Apple I still cannot login. The same happens if I try to sync my user with IFTTT. Question - How can login using my hidden email without "Sign in with Apple" option?

[Re-Titled by Moderator]

Original Title: Can't login using my hidden email