Can’t install 360 games digitally through the xbox store

Some games you will not beable to download from the store becuase the companies have not released them digitally only on discs.

Having the same issue . I purchased a gift card but the store says i have no valid payment options

That typically comes up if you're on a child account and trying to make a backwards compatible purchase through the One or website. If that is the case, you would need to make the purchase on a 360 console. Otherwise, make sure you have a credit card or
Paypal on file to make the purchase.

The One/website have never been updated to see the Microsoft Account balance as a valid payment option for backwards compatible content. You need a credit card or Paypal on file to make those purchased from the One/website. The Microsoft account balance
would only be seen as an option on the 360 itself.

I bought a disc copy of Batman: Arkham Origins a backwards compatible Xbox 360 game and I used to be able to see it for sale digitally on the Microsoft store, but ever since I installed onto my xbox via disc i can’t see the game itself in the store,
I can only see the add ons. Any reason as to why this is happening? I’d like to own it digitally instead but the digital game page is nowhere to be found.

What you mean with "for sale digitally on the microsoft store" ?

If you have the original disc in your tray, the console start downloading the Xbox One version.