When creating users, authentication should be based on their email addresses, which must be unique, instead of their usernames.

[IvanParvanovski]

When attempting to create a user with a unique email address, I encountered an exception because the specified username was already in use by another record. The exception indicated that a unique username is required.

_IntegrityError at /accounts/sign_up/ duplicate key value violates unique constraint "accounts_app_customuser_usernamekey" DETAIL: Key (username)=(Ivan Parvanovski) already exists.

It should be unique email address not username