We have resolved please see below
Dear ADRIAN HEAVEN,
Thank you for contacting Western Digital Customer Service and Support. My name is Gianni.
By reading your email, I understand that you are not able to erase your WD external drive under Mac OS HIgh Sierra. I do apologize for this inconvenience.
Please follow instructions listed on the article below on how you may erase your drive under this operating system. Please note that instead of the option ‘‘convert to AFP’’ you should just select ‘‘Erase’’:
How to Convert a WD External Drive to Apple File System (APFS) Format ~on WD Website
If you have any further questions, please reply to this email and we will be happy to assist you further. Western Digital wishes you a Happy New Year!
Western Digital Service and Support