Best thing to do right now might be to try editing the current file back down to $6 and see if that restores access, but I don't think it will work since my download link takes me to 0.2.9.2.
Based on an admin post, this is Itch's problem with implementing a system that works different than how many devs use it. https://itch.io/t/3930433/individually-priced-files-in-preventing-access-in-game...
The big problem is using it to have your game show up in the free games section, and using a paid file as the full game. Itch intended it to act like "DLC" for a game that already has a base price of $6 so you would just pay $1 extra for a separate file, or just raise the base price to $7 for new buyers without affecting previous buyers. They don't make that clear on the actual interface for uploading files and setting price, it's in a support document. https://itch.io/docs/creators/pricing#purchase-tiers-through-individually-priced...
What devs and users need to do is complain to Itch to allow users to increase an existing donation to a file, but I doubt they'll do anything because they'll say "we tell you in the support documents", and it looks like people have been complaining for years in multiple threads...