When I changed my mobile (i.e. Android OS Sony Z2), it couldn’t be connected through the My Cloud apps anymore. The error message is always “wrong password” but it is no password set-up.
The device might not be successfully paired with the My Cloud drive.
Please review and retry the steps on the following article:
How to access files on a WD My Cloud, Mirror, EX2, or EX4 Personal Cloud drive using WD My Cloud Mobile App