A check for ITVX
Use the exact programme and episode listing when deciding between live and catch-up. If the phone plays the episode and the TV shows no listing, check both the app and the edition of the service before changing an account that works elsewhere.
Check on the intended screen
Open the app catalogue on your actual device and confirm the publisher and region. Sign in only through the service or documented billing issuer.
Keep a title-level test
Use one title, episode or fixture that you can identify. Record whether the app launches, the account signs in and the item plays.