I had the same problem, from the iPhone the Stadia app does not let me play or link my account with the CCU. I solved the two in different ways: 1.) To play on the iPhone I opened the Stadia website...
See more...
I had the same problem, from the iPhone the Stadia app does not let me play or link my account with the CCU. I solved the two in different ways: 1.) To play on the iPhone I opened the Stadia website in the safari browser and I logged in using my credentials. Then you can play using your iPhone also works with a Controller. For easier access, you can add the Stadia webpage to the home screen. 2.) Linking my account with the CCU I had to use an android phone, I don't know why it didn't leave me to do it with the iPhone but after this, I was able to use the Stadia app on my iPhone to launch the games in the CCU.