I went through a big ordeal testing the device I was working with and led me to abandon this option. I don't remember what the exact problem was, but here are the issues I ran into as a whole.
- The firewall was blocking the port at first
- The certificates were not loaded correctly (I'm a CA novice). I ended up reusing the self-signed cert from Ignition's https config in Distributor.
- The device did not support non-TLS comms so 1883 would not work.
- The device I was using did not follow Sparkplug B spec completely.
My best guess would be to make sure you have credentials loaded to connect to Distributor.
This link should be a good place to verify your settings.
Getting Started: Two Ignition Architecture - MQTT Modules for Ignition 8.x - Confluence