Xbox Game Streaming (Preview) for iOS is expiring soon.

Until the iOS Smartglass gets a new update then the only way to do it is via Xbox.com store ( desktop version ) of your phone. I tried it during update preview, it works. Hopefully the iOS update comes soon to make it easier.

news.xbox.com/.../xbox-microsoft-unleashes-xbox-one-backward-compatibility-game-streaming-in-preview

Hi ClaimingDuke263,

Have you been accepted onto the Xbox Console Streaming (Preview) program? This should be found in the Insider Content section of the Xbox Insider
Hub app. I have quoted the below from the Xbox Console Streaming (Preview) program FAQ found at the bottom of the page.

“To participate in the Console Streaming (Preview), download the “Insider Hub” app to your Xbox One console. Then, download the “Xbox Game Streaming (Preview)” app on your Android device. Follow the steps in the app on your mobile device to pair your
console and phone. Then, start playing the games you already own! Please note, the initial roll out to Insiders will be phased. For the most up to date details on which Insider rings have access to the Preview, please visit insider.xbox.com.”

The xCloud preview is already out for iOS as announced by MajorNelson:

https://majornelson.com/2020/02/12/project-xcloud-limited-ios-testflight-preview-begins-today/

Project xCloud and the Streaming Preview was only originally available to those who signed up to test it in advance a few weeks ago. As of right now the streaming preview is only for Xbox Insiders who are in either one of the Alpha previews. i don't believe
it has trickled down to the Beta ring yet, and it will most likely leave its preview stages before it trickles down to the other rings in the Insider Program. By then, the Game Streaming preview will most likely be running in bigger test sessions.

You can learn more about it here.

https://www.xbox.com/en-US/xbox-game-streaming