Your is usually the email address you used when purchasing a license or signing up for a trial. If you have a Maxon account (Red Giant is now part of Maxon), that same email and password should work.
> ACCESS GRANTED. WELCOME, ADMINISTRATOR.
📍 If your ID works but the "Red X" won't go away, try clicking "Refresh" in the Maxon App or clearing your plugin cache in After Effects.
Your Red Giant ID is now a Maxon ID. Use the Maxon App. Keep your recovery email updated. And when in doubt, reset—don’t reinstall.