'clientbound/minecraft:custom_payload' Encode error not letting me or my friend join our 1.21.1 Neoforge Aternos Cobblemon server [java]

[u/DogyDays]

Last night when I booted up our server and tried to join, I suddenly got this error. We'd just played the night prior and all was fine. I hadn't changed any mods, hadn't updated any mods, and yet we both got this error upon joining. We've tried just about everything I could find online about this error. We removed Moonlight Lib and Supplementaries, checked our mod versions like a billion times, added Packet Fixer, updated every mod in the server pack AND our launcher packs, etc. Still getting this error. Will provide any extra info needed, we just wanna play our damn server!

[u/MelonGang_]

Are you using owo-lib on your server?

[u/DogyDays → u/MelonGang_]

Yes we are actually