Server not crashing but I can´t enter

I have created a server to play Minecraft with my sister and I keep getting this message when I try to enter my server: Internal Exception: io.netty.handler.codec.DecoderException: java.lang.IllegalArgumentException: Unknown recipe serializer twilightforest:transformation_powder.

Do you guys know why?

Quote from Roman

Such issues usually occur if the players who try to join the server don't have the exact same collection of mods installed on their computer as the server.

Note that also the versions of the mods must match.

Thanks!! I'll try that!