Unable to remote backup from EX4100 to WD My Cloud

Hi, New here and not greatly technical. Have been having significant problems trying to get my EX4100 to backup to a new My Cloud 3TB. After setting up the ssh and port forwarding as per the instructions, early attemps gave error messages ‘rsync test failure’ and ‘ssh password’ errors.

After much shenanigans, I now seem to be able to ‘connect’ with the My Cloud using the NAS selection and its IP address in the EX4100 remote backup dashboard, but each time I try to select a destination folder on the My Cloud I get the message; ‘Invalid Remote Backup Password. Try again.’

Strangely, it does seem possible to set up a remote backup from the My Cloud to the EX4100! Exactly the opposite of what I need.

Reading some of the posts here and elsewhere it seems the older versions of the My Cloud were not compatible with the EX4100 but the latter versions should be ok.

Firmware version on both devices: 2.21.126

Surely it must be possible to backup from the EX4100 to the My Cloud???

Is this likely to be something I havent set correctly?

Anyone able to help or offer possible solutions. I need to find the answer fairly quickly as if it is not possible, the My Cloud will be heading back up the Amazon!