Sometimes it becomes necessary to configure data transfer between two mqtt brokers. Such functionality is, for example, in Mosquitto MQTT Broker called bridge. This functionality allows you to forward messages from one broker to another, thereby having a copy of the data in two brokers.
Here is an example of setting up a bridge to send data from local topics zigbee2mqtt/# to mqtt.flespi.io:
topic zigbee2mqtt/# out 0
Files root.crt and certificate.crt you can get from Google Chrome browser: