This mod brings modern forwarding to Forge servers (See: https://docs.papermc.io/velocity/player-information-forwarding)
This mod also brings command argument wrapping which fixes this Velocity error: io.netty.handler.codec.CorruptedFrameException: Error decoding class com.velocitypowered.proxy.protocol.packet.AvailableCommandsPacket
Note: Latest version (> 1.1.7) of Ambassador doesn't require this mod anymore but you can still use it if you want modern forwarding.