Test one change at a time
Record the exact player name and device for both attempts. Where possible, test on the same network to avoid changing network and hardware together. If the second player needs a portal and the first uses a playlist, ask the provider which setup it supports for the new app.
Read the error in context
An immediate field validation error suggests the form or address syntax. A rejection after connecting can come from expiry, account permissions or concurrent use. A login that works while playback fails needs a playback check instead of a password reset.