Officially? No it is not possible to access the My Cloud in the way you are attempting.
Unofficially? The My Cloud Dashboard generally rejects any attempt at Dashboard access from an IP address outside of the IP address pool it is in. However, there are other ways to access the My Cloud remotely from using insecure FTP to using SFTP to using SSH. For those using the older generation single bay My Clouds that use v4.x firmware they can install and run the CloudDAVMod app. Many if not most of these methods require using SSH to modify the firmware to allow for such access. There are discussions on those options that can be found using the forum search feature, magnifying glass icon upper right. Here are some discussions. Note: WD does not support such unofficial methods of remote access.
https://community.wd.com/t/app-clouddavmod-various-versions-for-firmware-v4-09-2016/161543
https://community.wd.com/t/how-to-setup-sftp-on-my-cloud/152297
https://community.wd.com/t/how-to-access-dashboard-remotly-throgh-browser/147803/4
