I have an invite code

You probably don't need it.

When a board or a landlord adds you, they add your email address. Signing in to the app with that address is all it takes — no code, no form.

The code is for two situations:

You want to sign in with a different email address than the one they have on file.
You were handed a code on paper — a letter, or a card at the mailboxes — and there's no email involved.

In either case: open the app, tap Have an invite code? on the sign-in screen, enter the code, then sign in with whichever address you like. Already have an account? Tap Have an invite code? on the welcome page instead. A code makes one new account, is good for 30 days, and can be renewed by whoever sent it.

A code used from a different address is reported to the board — not to stop you, but so they can confirm it reached the right person. Communities are small; that's the whole safeguard.

Already invited? Sign in with the email address your board or landlord has on file; the invitation email has the link.