AutoModpack

Most Minecraft proxies drop the early login packets AutoModpack uses, so a standard proxy setup breaks the modpack connection. The proxy has to forward those packets.

ProxyStatusSetup
VelocityWorksNeeds a patch plugin and MAGIC
Gate LiteWorksPort configuration
GateFails
WaterfallFails
BungeeCordFails

Velocity

Velocity does not forward the packets on its own. Install the official AutoModpack Velocity plugin and set connection-mode to MAGIC.

Gate Lite

Gate Lite forwards the packets out of the box. What needs care is routing: the client dials the advertised endpoint, controlled by advertised-endpoint-host and advertised-endpoint-port, and that route has to reach the backend in a shape the selected connection mode accepts. It does not have to match the backend's bind-address or bind-port.