iMac (Retina 5K, 27-inch, Mid 2015) Login problem...

We are resetting an iMac (Retina 5K, 27-inch, Mid 2015). I am at the screen asking for a verification code. Nothing has arrived at either my phone number or email address. I have no other Apple products, however I can login to iCloud, iTunes and here at the Apple Community and receive verification codes whether logging into the apps or in a browser. I just can't get one when I log into the iMac.