Can't buy gamepass

Ummm that only applies to xbox games he is talking about PC

NO you don't need gold or gamepass HOWEVER if you want to play it but not buy then gamepass is needed

And you can buy it at a discount with gamepass to keep it otherwise you can't play it after gamepass expires

Now if you buy it separately no gamepass isn't needed

For such cases, we recommend the basic troubleshooting steps such as restarting your device and your router as well.

If you are facing the issue with the purchase itself, I suggest checking this link Get help with purchase errors | Xbox Support
However, if the issue still persists, you will need to contact our live support Contact us | Xbox Support to check from their end.

Hi. My name is Brilliant and I am happy to assist you today.

You can check if online purchases are enabled on your bank account. Check if your card online purchase limit meets the required funds for the purchase. You can also try to purchase using a different device or browser.

I hope this helps resolve your query. Happy Gaming.

Regarding your issue, I would highly recommend contacting the support through: Contact us | Xbox Support

They shall assist you!

If you got it free off the game pass but then stopped paying for gamepass, you can't play it anymore. Also if it goes away from the gamepass menu, you'd still need to buy it.