The account owner is also getting the same error when they try to refresh the campaign from the settings window where you set up the link between patreon and the game on itch.io.
That’s a separate issue. Patreon’s API is returning HTTP 403. Either Patreon is at fault here, or perhaps the account owner deleted itch.io from the list of connected apps from the Patreon side? If they disconnect and reconnect on itch.io then it may solve that: https://itch.io/user/settings/connected-accounts