Am I wrong in assuming that this is a client-side mod? And so it shouldn't need to be installed on the server. I get this error.

[21Apr2021 18:38:41.838] [Netty Client IO #2/ERROR] [net.minecraftforge.fml.network.NetworkRegistry/NETREGISTRY]: Channels [imm_ptl:main] rejected their server side version number during listping
[21Apr2021 18:38:41.838] [Netty Client IO #2/INFO] [net.minecraftforge.fml.client.ClientHooks/CLIENTHOOKS]: Client has mods that are missing on server: [fallingleaves]
[21Apr2021 18:38:46.996] [Render thread/INFO] [net.minecraft.client.gui.screen.ConnectingScreen/]: Connecting to localhost, 25565
[21Apr2021 18:38:47.783] [Netty Client IO #3/ERROR] [net.minecraftforge.fml.network.NetworkRegistry/NETREGISTRY]: Channels [imm_ptl:main] rejected their server side version number
[21Apr2021 18:38:47.783] [Netty Client IO #3/ERROR] [net.minecraftforge.fml.network.FMLHandshakeHandler/FMLHANDSHAKE]: Terminating connection with server, mismatched mod list