It looks like the mod ctm, which I believe is "ConnectedTexturesMod" is missing (from the server? Or maybe you need to remove it from your computer?). I see the error:
Attempting connection with missing mods [ctm] at SERVER
I believe this log is your Minecraft client, can you share the server log as well?
Here's a link to the mod: https://minecraft.curseforge.com/projects/ctm?page=3
Here's a guide that explains more about missing mods: https://shockbyte.com/billing/knowledgebase/65/How-to-Fix-Missing-Mods-MissingModsException.html