Custom Map Consistency Errors
Did you already have this error when you tried to connect on a versus game to play a custom campaign despite having exactly the same version than server or local host?
Server is enforcing consistency for: customcampaign.vpk
You are at the right place.
This is simple like hello. If it happens this is probably only because the filename is different than what it is on the server or on the computer of the player that is hosting, indeed it will prevent you from joining with a consistency error.
It can easily happen if one player downloaded the map from workshop because filenames are only numbers, and if others took the map from another source.
In case it was still not clear everyone need the same filename for the custom campaign.