I tried to create an account on Bet25 and I got an error saying "Invalid email address", even though my email address was valid.

After reloading the page and re-entering my email address a few times, I finally remembered that I had already created an account on Bet25, and that was why I was getting that error.
It would be much better if you displayed a different error message when someone tries to register an account with an email address that has already been used.
Should next something like this happened then you should know that there is a double space on it.
I have actually experienced something like this on casino back then when trying to login, I didn't know I had double space on email address, after every I tried to rectify it and login.
That is right, it would be better the team gives a different error message like 'this mail has already been associated with this site' than for someone to keep entering same mail and it gives error without specifying the error codes.