ERROR when trying to buy xbox 360 games on Xbox One store or xbox.com

My account on my xbox one is a child account too and I am having the same problem. I have an xbox one with xbox gold subscription. I do not have access to an xbox 360 so how can I get the free xbox 360 games with gold on my xbox one? I don't have any problem
getting the xbox one games, just the backward compatible 360 games. the message tells me to complete the transaction on my xbox regardless of whether I am on my xbox already or on xbox.com on my laptop. Help please! we want the 'free' games that we payed our
subscription fees for!

Is your account a child account? If so the only way for you to purchase/claim any content (even free content) that is either an Xbox 360 game or an Avatar item is an actual Xbox 360. You should be able to use its store interface without any problems.

When you select the Xbox 360 Games with Gold on your Xbox One console, they will appear on the Xbox Store but that does not mean it won't be an Xbox 360 game. Selecting 'Show price' and then proceeding to "buy" the game (in these cases you'll be "paying"
$0.00) will add the license to your account.

Have you tried downloading these games from the
Xbox Games with Gold page on Xbox.com instead of your Xbox One console? Are you recieving any errors when you attempt?

Lastly, we recommend that you try uploading any screenshots to OneDrive so you can link us to the picture in this thread. Thanks!

Are you trying to buy a backward-compatible Xbox 360 game on Xbox One when you get this error, or are you trying to buy Xbox 360 content on your Xbox 360 when you get this error?

Translating to Portuguese using bing.com/translate:

Você está tentando comprar um jogo Xbox 360 compatível para trás no Xbox One quando você recebe este erro, ou você está tentando comprar conteúdo do Xbox 360 no seu Xbox 360 quando você recebe este erro?

Randy, with me, it happens when I try to buy a backward-compatible xbox 360 game on my xbox one, or using the computer or cell phone. I don't have a Xbox 360.

H Ak on the floor, yes if you buy Battleblock Theatre from the xbox store (Xbox 360 section) on xbox.com, when you log in on Xbox Live on the Xbox One, it will show in the ready to install section in my games & apps, just select it, and start the install.