Hi,
After buying the game, you would need to "Claim the Game" to link the purchase to your itch-io account.
https://itch.io/docs/buying/already-bought
I have successfully claimed and permanently linked my own Itch account, and my orders and download permissions are fully functional now.
Let me walk you through the entire process and the issue I encountered:
1. I launched the game normally and clicked the [Login] button in-game.
2. I was first redirected to itch.io, where I copied and entered the token as instructed.
3. After entering the token and confirming, the page automatically redirected me to the Patreon website for authorization.
4. I granted the requested permissions, completed the whole process, and returned to the game as prompted.
5. Upon returning to the game, I still saw the message "Game not yet purchased " and was still unable to unlock and access the full game.
Could this be because I have never subscribed to your Patreon tier? I only purchased this game via itch.io.
I hope this issue can be resolved as soon as possible.