Mods not working in servers?

Last week me and my friend were able to play servers with our mods just fine but today we haven’t been able to get them to work. Not to sure if I missed something or if they just aren’t working.

You can only use the mods the server you join has. If you use a modded car that is not on the server it won’t let you spawn it, or if it does, the other players won’t see you.