# X_TRANSPORT_PROTOCOL

## Means

the bus does not speak the protocol this build speaks

## Typical cause

nats-server older than 2.11, JetStream not enabled, or something that is not NATS on the port

## Fix

run `nats:2.11-alpine` or newer with `-js`; reconnecting cannot fix it, so this never retries

[Realtime](/error-codes#realtime)