There are (at least) two possible Thing structures
Yours -
Bridge mqtt:broker:pibroker ... {
Thing topic sonoff11 ... {
Channels:
Type switch ...
}
Your topics implicitly “belong” to that broker Bridge by being nested in it’s curly brackets.
But these topic things
Thing mqtt:topic:flomqtt:MQTT_FSD_A "FSD 'A'" (mqtt:broker:flomqtt) {
Channels:
Type switch : ...
}
This is not nested in the broker Bridge definition, it stands alone. (maybe the broker is defined in a different file, for example)
So it has to describe which broker it belongs to (you’re allowed more than one)