Custom Phone Authentication.

I am trying to create a custom phone authentication. Users will input their phone number and in the next page they will have to enter the OTP to verify their phone number. I am using my local sms service provider to send the sms. Now the question is that after all this screen flow, I want to create the new user in the users collection. But I am seeing this message "Can only create a "users" document via an Authentication action." Any workwround solution to create the users? I dont want to use sign up with email option.

Thanks in advance.