Problems adding new user for cloud access

Please let me know if there is already another discussion around that topic - but:
I own a MyCloudEX2Ultra on OS 5 (unfortunately). I have set up everything and it all works more or less fine with my Android photo backup and so on.
I try to add my girlfriend for cloud access by sending that email.
Email recieved, link clicked - and the answer always is, that the owner of the system denies the access.
We tried 2 different emails, replying immediately afte receiving the email, even being logged in as an admin meanwhile - nothing works.
Official customer service sent me a standard reply emails as an answer - not very helpful.
What else can I do???

There are two ways for you to check that, first, use the search icon at the top of this page or second, check the Knowledge Base.

You have posted in the WDMYCLOUD sub-forum.
I doubt if we’ll ask a question about the EX2 Ultra.

My Cloud OS 5 Online User Manual (