After meshtastic 2.3.0 mqtt protobuf messages come in at msh/+/c but MQTT node in the "Ingest from MQTT" subflow subscribes to msh/+/e
-- from meshtastic documentation
Protobufs topic
A gateway node will uplink and/or downlink raw protobuf MeshPackets to the topic:
msh/2/e/CHANNELNAME/USERID, where CHANNELNAME is the name of the channel (firmware versions prior to 2.3.0 will publish to a topic with /c/ in the place of /e/).
For example: msh/2/e/LongFast/!abcd1234