Xbox (beta), can't see purchase options

This screen appears) No options to buy anything...

What happens when you click on the 'Join Game Pass' button?

Are you in the beta? Cause if you're in the beta, DLC should be showing a cash amount and not points when you go to purchase it. When you go to purchase something, select "Manage payment options" and see if there's an option to select your Microsoft account.
When you redeemed the 800 points did it tell you it was converted to a cash amount after you confirmed the redemption? Also, you'll probably get better help by posting this in the beta support forums, if you are indeed in the beta.

Hi, things work very strangely when it comes to backwards compatible titles and payment options added on an Xbox One, for whatever reason you can't use a payment option to purchase these games if you added it on an Xbox One, you have to add the payment option
on an Xbox 360..........funky huh

https://support.xbox.com/billing/payment-and-purchases/troubleshoot-xbox360-marketplace-purchasing

I added a payment option to my account at account.microsoft.com or on my Xbox One console, but I don't see the payment option when I try to purchase.

If you don't see the payment option when you try to make a purchase, you need to add
the payment option on your Xbox 360 console.

To use currency, you'll first need to select your Microsoft account as a payment method. When you go to purchase something, on the confirm purchase screen, select "Manage Payment Options" then select Microsoft account and you'll be able to see how much you
have total and be able to purchase content. If you don't see the option for your Microsoft account, then that's a whole different problem entirely and I'm not sure they've fixed it yet.

Also, are you still having problems accessing the beta forums? Did you follow my instructions above? Here's the link to the beta forums:

http://forums.xbox.com/xbox_forums/beta-2013/default.aspx