Can't add users to my Premium for Family account

[keithbash]

Plan

Premium for Family

Country

U.S.

Device

PC

Operating System

Windows 10

My Question or Issue

 I'm the owner of a Spotify Premium Family account.  I have installed in my house a multi-room audio system and CasaTunes, a software application tha supports 3 mediaservers that can play music in any room.  Each CasaTunes mediaserver can use Spotify as one of its music program sources, but the Spotify account each mediaserver is using must not be the same as Spotify account that either of the other 2 mediaservers is using.  I'm trying to set up 3 Spotify user accounts as members of my Spotify Premium Family account so that I can specify them to CasaTunes as the Spotify accounts to be used by its 3 mediaservers.  I have 2 Spotify Free accounts set up and can log into them; their associated profiles (limited info notwithstanding) seem OK.  I'm unable, however, to add the those users/accounts to my Spotify Premium Family group.  I issue the invitation to join to those email addresses and log off Spotify When I reply (from the email addresses associated with those accounts) to the invitation to join the family plan, submitting the confirmation page results in "603 - Oops something went wrong, please try again."

Can you help me?  What am I doing wrong?

[Jᴀᴄᴋ]

Hey @keithbash thanks for reaching out to the community,

Try these steps and maybe I can help you figure this out: 

1. Try a different network connection or try it on a different device.

2. Try a clean reinstall on your device.

3. Try a different browser or incognito mode.

If these dont work, let me know, or you can check out this Premium for Family support article on Spotify's support page.

Happy listening,

-J