First, you may want to post to the dedicated My Passport Wireless subforum where there are probably more knowledgeable users, as this subforum (My Cloud) is generally for the single bay My Cloud devices.
Second, the MyCloud.com is an online web portal for users to remotely access certain WD devices that allow for remote access. It is NOT the website where you “register” your device with WD.
It is not clear that the My Passport Wireless Pro even needs one to access the MyCloud.com web portal to create an account. Instead the User Manual talks about using the My Cloud mobile app to access the device on the local wireless network. See Chapter 3 Setting Up The Wireless Drive, Using WD My Cloud App on a Mobile Device in the User Manual for more information.