# MQTT Transmitter unable to connect

**URL:** <https://forum.cirrus-link.com/t/mqtt-transmitter-unable-to-connect/883>\
**Category:** Ignition Modules\
**Created:** [September 11, 2026, 11:56pm UTC](https://forum.cirrus-link.com/t/mqtt-transmitter-unable-to-connect/883 "2026-09-11T23:56:33Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![eric.olson](https://avatars.discourse-cdn.com/v4/letter/e/74df32/32.png) [@eric.olson](https://forum.cirrus-link.com/u/eric.olson)\
**Post date:** [September 11, 2026, 11:56pm UTC](https://forum.cirrus-link.com/t/mqtt-transmitter-unable-to-connect/883/1 "2026-09-11T23:56:33Z")

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We are just starting our MQTT journey and I’m trying to just establish a connection to our MQTT broker and publish/subscribe to some tags to establish everything is working. I’m using Azure Event Grid as the MQTT broker. I have been able to subscribe and publish to some test topics using the Mosquitto utilities. With MQTT Engine, I’ve established a connection and it’s sitting there as Connected.

My problem is with MQTT Transmitter in Ignition. No matter what I do, I get a warning “connect failed due to Not authorized to connect” and then an error “Failed to achieve connected state”. I’m using certificates for authentication, which I’ve uploaded to the Certificates tab and added to the MQTT server definition.

I’m at my wit’s end. Does anyone have any suggestions as to what might be wrong?

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**Author:** ![wes.johnson](https://avatars.discourse-cdn.com/v4/letter/w/f14d63/32.png) [@wes.johnson](https://forum.cirrus-link.com/u/wes.johnson)\
**Post date:** [September 12, 2026, 11:12pm UTC](https://forum.cirrus-link.com/t/mqtt-transmitter-unable-to-connect/883/2 "2026-09-12T23:12:40Z")

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The connection settings should be exactly the same for Transmission as they are for Engine. I would suggest checking them one more time. It might be worth trying the Engine certificate on the Transmission connection to verify the basics since you know those creds are good. If you fail to get connected after this, I’d recommend sending and email to [support@cirrus-link.com](mailto:support@cirrus-link.com) so we can jump on a quick call with a screen share to debug this together.

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**Author:** ![eric.olson](https://avatars.discourse-cdn.com/v4/letter/e/74df32/32.png) [@eric.olson](https://forum.cirrus-link.com/u/eric.olson)\
**Post date:** [September 14, 2026, 5:15pm UTC](https://forum.cirrus-link.com/t/mqtt-transmitter-unable-to-connect/883/3 "2026-09-14T17:15:10Z")

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Got it resolved. It was that the topic space in Azure did not contain the Sparkplug “spBv1.0/” prefix. I think the Transmitter publishes the LWT when it connects, and it did not have permission to publish on that topic. Engine doesn’t publish anything on connect, so it didn’t experience that problem.