Battlefront cross compatible.

If you're on a child account, you'll need to make the purchase from a 360 console. Otherwise, make sure you have a credit card/Paypal on file in order to make the purchase.

Hi there GrubbyScarab, thanks for reaching out.

This error message means that the Microsoft account you're using to attempt the purchase doesn't have the ability to make the purchase due to being on a Child or Teen account. Child/Teen accounts are prevented from making purchases
in the Xbox 360 Marketplace. More info about this on our
Troubleshoot Xbox 360 Marketplace purchasing support page.

Something you can try is logging into your account and purchasing the game directly from an Xbox 360 console.

What about the original Star War Battlefronts? Love to play those again fingers still crossed for backwards compatibility as my Xbox original bit the dust last summer.

That game is already backwards compatible. https://www.xbox.com/en-US/games/backward-compatibility

There's also the Star Wars Battlefront Collection that's releasing next month that includes it also. https://www.xbox.com/en-us/games/store/star-wars-battlefront-classic-collection/9PDKZCQ8J879

The SW Battlefront 1 and 2 have a xbox one version, while the unleashed are only 360 games, playable on xbox one by backward compatibility.

You are redirected to 360 on the battlefront titles too?