Direct answer

Velocity’s current FAQ says this typically occurs on Spigot-based backends when a modded client connects. On Paper (or a Paper fork) 1.12.2+, the documented workaround is the startup flag `-Dpaper.disableChannelLimit=true`; also verify the modded-client/proxy/backend combination is otherwise supported.

What it means

Velocity documents this as a common incompatibility when a modded client connects to some Spigot-based backends.

If you are a player

  • Copy the exact connection/kick message and note the timestamp; similar-looking login errors can have different causes.
  • Check the address, port, Minecraft version, and whether other players can connect at the same time.
  • Tell the owner whether the problem follows your account/device/network or affects everyone.

If you run the server

  1. Confirm the backend is Paper/Paper-compatible and the error exactly says Invalid payload REGISTER.
  2. If applicable, add -Dpaper.disableChannelLimit=true to the backend JVM startup flags and fully restart it, as documented by Velocity.
  3. If the error persists, compare the modded client, proxy, backend version and plugin-channel/protocol plugins rather than changing unrelated forwarding settings.

Important notes

  • Packet exceptions often wrap the real cause. Keep the full nested exception and identify the first plugin/mod/protocol component named in it.

References

Use the documentation for the exact software and release you run. These sources support the settings or diagnostic behavior used in this fix.

Focused diagnostic check: Determine whether the connection is to a Velocity proxy or a Paper backend and record the plugin that sends the REGISTER payload. A BungeeCord-targeted plugin is not automatically a Velocity plugin, and a Velocity plugin does not belong in Paper's plugins/ folder. Reproduce after temporarily removing the suspected proxy-side integration from a staging copy.

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