Setting up shared user

I have set up my base alarm and all is working fine. I’ve added family members as shared users, but one does not work. After setting up his account, downloading the app, and entering his confirmation code - the app doesn’t display anything (no devices). We have deleted and re installed the app and re set up his account... but same problem. Two other family members have followed the same steps to be set up as shared users and all worked fine. Any suggestions what might be different with this third attempt that won’t work?