Issue of the topic: I’m preparing a new version of the Openhabian to communicate with Sonoff R1 and R2, with Mosquitto.
Mosquitto is working well, as demonstrated in this figures.
You’re probably using some old tutorial about MQTT binding version 1
MQTT version 2 binding uses quite different configuration, with Things and channels.
You need to be consistent about which you use.
If you want to be offered version 1 bindings in the list, I think you need to configure “enable 1.x legacy bindings” in PaperUI > Configuration > System
Or else you need to learn how to configure MQTT binding version 2.
You may want to consider moving to the mqtt version 2 binding. You can use both versions and move devices one at a time. IMHO the V2 binding seems to work much better. If you like I can post some examples, although the forum has many, to help you get started.