Some users may be unable to currently purchase backward compatible content on Xbox Live, according to Microsoft.
The Xbox Live status page notes that the issue appears to be with backward compatible content purchased through the Xbox One, advising players instead to buy content through the Microsoft website.
“We’re aware some users are unable to purchase backwards compatible content on the Xbox One. While we investigate the issue, please purchase this content through the Microsoft Store website,” the status page reads.
“Our engineers and developers are actively continuing to work to resolve the issue causing some members to have problems purchasing content. Stay tuned, and thanks for your patience,” it continues.
Source: IGN.com Xbox Live Currently Experiencing Game Purchase Issues