Is this an error or do I have to pay again for the same game I already bought?

You don't need to buy the game again.

Basically the system goes like this:

If you just buy a game you can stream it from your console to your phone/tablet etc. for free. However if you want to stream it from Microsoft own servers you require Games Pass.

The problem is that most peoples internet isn't good enough to stream a game from their own console, so its up to you how you go from here, either play the game locally on your console or pay the charge to stream it from Microsoft.

Hi and thanks for reaching out. I hope you’re doing well. I'm an Independent Advisor and a Microsoft user like you and I'll be happy to help you.

I understand you need assistance with your game. Just to confirm, are you playing on a PC or Xbox console?

Hello, does it show that the money was taken out of your account for the game?

For the first time you brought it? Was their any returns of that money later on down the line??

If it doesn't show in your download history then that usually means it wasn't purchased on your account. You would have to make sure you're signed in to the account that purchased it in order to redownload it. If you're 100% sure that it was your account that purchased it and it's not showing in your download history, you will need to contact support.