Maybe the game is locked in your region , the only way i found to purchase 360 games recently is adding funds to my account and purchase it either from the 360 or the xbox one , if the game is region locked you have to use a vpn to install it to your xbox 360 there is no region lock for 360 games or any game on xbone

Yes, all backward compatible Xbox 360 games are still playable on Xbox 360. On the other hand, you need to be careful with buying backward compatible OG Xbox games on Microsoft Store (xbox.com, NOT marketplace.xbox.com) because not all of them are compatible with Xbox 360.

If you still worry about it, buy it on Xbox Marketplace, which is for 360 only : https://marketplace.xbox.com/en-US/Product/MCLA-Complete/66acd000-77fe-1000-9115-d802545407f8

That's been happening since last dashboard update from what I have read.  You have to put the money into your Microsoft account and transact out of there when it happens, apparently.

It also won’t let me buy it through the console. No matter what card I put in it always comes up with an error.

Anyone know if I buy the game here it’ll be playable on my 360? It only says its playable on the One and Series X/S despite having the 360 name on the thumbnail and I’m a bit skeptical.