# X_APP_URL_PORT_MISMATCH

## Means

APP_URL names a loopback port x dev does not serve

## Typical cause

APP_URL is a localhost origin whose port is not the one x dev binds (--port, then PORT, then 3000), so OAuth redirects, absolute links and the sync origin point at a server that is not this one

## Fix

`export APP_URL=http://localhost:3000`

[CLI and verify](/error-codes#cli-and-verify)