Why can't I add a new travel companion to my Reservation Service profile?
If the traveler you are trying to add bought their Pass at Eurail.com or Interrail.eu and has a different order number to you, then they need to register for their own Reservation Service account before you can add them to yours. They can do this by logging in to the Reservation Service using their own account.
Once your companion has logged into the Reservation Service, you can add them to your profile. When you see the question "Is your traveling companion already registered in the Reservation Portal with a currently valid pass?" click on the "Yes" option then search for their email address and order number.
You can check your and your travel companion's order numbers in the confirmation email you received when ordering your Pass. The order number starts with EU or IN.