I'm not sure about the PayPal vs Credit/Debit card setup as I just used my debit card to setup payment and didn't even think about using PayPal.
With regards to your friend and his iPhone not communicating with his Chromecast Ultra (CCU), perhaps check the following, as I assume based on him using a Buddy Pass that he already has a Chromecast Ultra rather than getting one by purchasing a Premium Edition or Founders Edition.
Note: Embedded/Integrated Chromecast Ultra devices are not currently supported to the best of my knowledge, just regular Google Chromecast Ultra devices are supported. I guess at some point in the not too distant future integrated CCU's will be supported, but not just yet.
1. Make sure that his CCU is running the correct version of code, latest version is best, but it must be version 1.42.180348 or higher.
2. Install both the Google Home app and the Stadia app on to the iPhone and Google Assistant if you plan to use it too.
3.Setup the CCU using the Google Home app first, it is recommended to use a wired connection for it, but use WiFi if not possible, and make sure that the iPhone and CCU are both on the same network.
4. Launch the Stadia app on your phone, link account and enter code, then choose your username and after that it's just a case of follow the instructions to get it all working..very easy..
Let us know if you still have any issues or need further explanation on anything.
Thanks Mad Dog 4 your answer.
We exactly did install the system like u explained now but it isnt working..
Seems not that easy..
There is a reset button on the Chromecast, the wifi of the stadia service and the phone / chromecast have to be on the same network
I can't new payment method in my new number