Cannot update from Yosemite as App Store won't accept Apple ID Password.

I have erased my mac, and it has reinstalled to MacOS Yosemite.

Now I wish to update to the latest possible MacOS. I have attached my Apple ID to the Mac, but the App Store does not accept my Apple ID password, leaving me unable to update the MacOS.

I have tried changing password without luck.

I am on a MacBook Pro (Retina, 13-inch, Early 2015)

Has anyone experiences similar issues when erasing? Are there any fixes?