Minecraft Forge Server error message when joining?

I created my own Forge server that runs on my pc. Port released, everything done as prescribed. As soon as I install mods, i.e. Copy mods into the mods folder for the server, I see: failed to synchronize data from server. Connection lost or something like that is not in front of the screen. How can I fix that? Have also tried where I had installed the mods clientside.

You must have installed most of the Forge Mods in the client and on the server. Both sides need exactly the same data, same version of the mods and same Forge version.

There are some mods that are only required on the client side. GUI mods or maps, for example, that do not belong on the server.

There are few mods that only belong on the server and are unnecessary in the client, admin tools e.g.

I already know everything that you have enumerated and have also tried it, but unfortunately this is of no use.