Please check as follows:
 

1. Confirm whether the user has an account of our App (sharing and adding a family must be in our App, not an account of Alexa or Google Home);
 

2. Please confirm that your account and the accounts to be shared belong to the same cloud server, and you can only share devices on the same cloud server;
 

Please open the App "Profile", click the user avatar at the top of the page, enter the "Account and Security" page, and check the “Cloud server”; if the accounts to be shared is not in the same cloud server, please switch the server.