Their casino there rules, I experience a similar challenge earlier today when I sign up at one new casino, I used the email option during registration but when I wanted to make a deposit and claim the welcome bonus, I was asked for a phone number, and by then I did not register with a phone number and when I try to update my phone number on the user profile edit page, it didn't works.

So I had to abandon the account and created a new one using my phone number instead of the email option, we need to be very careful when creating accounts on casinos because not all information can be changed after registration.