Passport wont back up on OS SIERRA

Since moving to OS SIERRA VER 10.12 my MacBook Pro won’t back up to the Passport.

The Mac recognises the Passport in through the USB and the Passport recognises the connection and lights up and whizzes away but I can’t start the back up. Any ideas anyone?

How do you run backups in your system? And which operating system were you using before you migrated to OS 10.12?

Hi there.
I was running whatever it was that came before SIERRA. I run the back up straight onto the WD PASSPORT. However, after I posted my query, I left the Passport plugged in and all of a sudden it started backing up!!! So dunno what to think really. It usually reminds me every ten days or so to back up again so I’ll see if it does the same thing again.
I’ve come across quite a few little things that I can’t get anymore since I upped to SIERRA. Bit of a pain really.
Thanks for getting in touch.