Support has about a 10 day backlog on their emails.
Official documentation makes no mention of the error message returned by the itch.io version of the game.
Some players have been spreading a claim that this error has been responded to on the official Discord. The information suggests that Innersloth is deliberately not providing proper support for the itch.io version of their game going forward.
My only (so far) email response from support has not clarified if this is the case, and I am waiting for another reply, hoping it doesn't take a long to continue the conversation as it did to start it.