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Recognizing that there many existing clients which are only compatible with the MQTT Sparkplug™ B specification v2.2, we have made changes to MQTT Engine to establish a now supports an MQTT client whose only function is to publish the STATE message in its legacy format.

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However, there are some instances where the migration from older MQTT engine Engine modules does not complete this process and it must be complete manually.

MQTT Engine will always attempt to publish/subscribe using the new STATE message format even when the Legacy Client is enabled and there is no means to disable this.

If you have restrictive Access Controls Lists configured at your broker you will need to allow access to the spBv1.0/STATE/ topic

completed manually.

How do I configure the legacy state message?

The additional legacy STATE client is configured under the Advanced section for each of the configured MQTT servers in the MQTT Engine module configuration. The Legacy State template will be automatically populated with the variables from the server configuration Main and TLS sections if you are updating from a previous version of MQTT Engine to v4.0.14.
For some MQTT servers, the Username/Password for each client connection must be unique and so these parameters for the second legacy client will need to be edited. 

To disable, you simply deselect the Enable Legacy STATE messages option. To fully remove the retained legacy STATE message at the server, you will need to restart any connected server.

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• ME client created, connects and subscribes [[a/#][0], [spBv1.0/#][0], [spBv1.0/STATE/MyPrimaryHost][1]]
• ME-LS client created, connects and subscribes [[STATE/MyPrimaryHost][1]]