Guessing that the person who posted this found a solution but I got to this post from Google when looking for a solution so thought I would post the fix incase anyone else runs into it and gets here.
Found the answer here: https://48web.com/cheatin’-uh-error-wordpress-custom-post-types/
Basically in the above example change:
register_taxonomy(
'Models',
to
register_taxonomy(
'models',
and you should be fine.
