Habe grade selbst nochmal im AppStore geschaut und man kann die App nicht mehr laden.
Hatte MS wohl was dagegen, dass es funktioniert hat!
Website: onecast.me/Microsoft have recently changed the way in which third party applications such as OneCast authenticate with Microsoft servers. Due to this, for the time being OneCast is no longer able to process new Xbox One registrations and as such we have made the decision to temporarily remove downloads for all versions of the app. We are currently working on updating OneCast to use the new authentication method, which when done will restore full functionality. At that time, we will reinstate all versions of OneCast (we aim to have this completed early next week). Please accept our apologies for any inconvenience caused.