Is there any way I can purchase the orange box

At this point you'd have to try to find it on disc. It was delisted a while ago.

Here we go Mr. Freeman!

Load disk, download the "update" (4.92GB, that's the game itself) and play on Xbos Series X.

Thanks. I know what you are meaning, but that's the list of the optimized games for this Series X/S gen. The Orange Box is a 360 game, optimized for Xbox One X (Xbox One X Enhanced), so backwards compatible, a game from previous generation (X360) playable on the Xone and also on the actual generation of console, thanks to the BC program of Microsoft. The game is not optimized for Series X/S, it would have to X/S logo like other games i own (Subnautica, We happy few etc). The only problem with this game is with the purchase from the Marketplace!

Yes, but in order to purchase it you have to go with the old 360 marketplace, click the buy button, appears next window with the method (card, paypal ecc) and the "confirm button". When i click it, starts spinning the wheel (the usual you see when you purchase anything) then nothing happens, wheel continues spinning and it never shows the "thank you for your purchase" message.

The game is definitely backwards compatible. There have been a lot of people having issues with purchasing backwards compatible games from the site, but I haven't seen a solution yet. Unfortunately the only other way around it is purchasing it from a 360.