When i log into my server this pops up

do you use a mod called apoli?

Make sure that the exact same mods installed on both your PC and the server. It is not enough to simply have the same mods installed, they must also be installed in the exact same version. Likewise, the version of the mod loader (Fabric/Forge) must be identical.

If you use a Modpack make sure you're running the same version as the server.

Just do what i said.