Log in with the account you just created
Sign in with the same email and password or simply use Sign in with Apple if you are using that for your account. Note: your membership is tied to this account. Alternatively, if you already have the app installed, open the Opal app, navigate to your profile, and select Sign Up.
If you encounter a paywall instead, tap "Restore Purchases," and when asked "How did you purchase Opal?", select "Web."