WD My Passport Ultra drive won't mount

It was formatted by my client for Windows, but I use Mac. I went to Mac Disk Utility to erase and reformat the drive, but as I hit enter to initiate that process the drive immediately unmount. I cannot get it to remount. My disk utility now recognizes the drive as “disk3s2”. Any ideas?

Hi JakePhotos,

PC formatted drives with a GPT partition, would cause the Disk Utility to unable to mount on macOS high Sierra. You can follow the steps mentioned in below article to reformat My Passport on macOS: