In Postman v12, open the project root /home/ryan/Media/Code/Code/robot-market/test-mqtt-5 using Files → Open folder, then select Local View. This MQTT collection uses Postman's v3 multi-file format; it is not a standalone file to choose from Import. Do not select the .request.yaml file or the nested collection directory in the Import dialog. Postman discovers the collection at postman/collections/MQTT Broker UI Test. Keep the observer container running and open http://127.0.0.1:8080 in your browser.

If you still get “We don't recognize this file” after opening the project root via Files → Open folder, bypass the saved collection and create the request inside Postman: click + → MQTT, enter mqtt://109.122.252.129:1884, set MQTT version to 5.0, enter the sim-001 test username/password under the request's connection/auth settings, and click Connect. Then follow “Publish a test telemetry message” below. The message's topic and payload are the actual test inputs; the MQTT collection file only pre-fills the broker URL and provides notes.

The older MQTT Test Viewer.postman_collection.json file is a Postman v2.1 HTTP collection with two read-only checks for the viewer page and /api/snapshot. The MQTT v3 collection below is for broker traffic. To subscribe to telemetry in Postman, use the test-backend credentials; device credentials can only subscribe to their commands topic. To publish as ESP32, use the esp32-lab-001 credentials and its matching topic path. Current Postman supports MQTT requests in its v3 multi-protocol collection format.

Quick functional test

Connect to mqtt://109.122.252.129:1884 with any existing test account (including esp32-lab-001) and its current password. Select MQTT 5.0 and use a unique client ID such as postman-functional-test-01.
Publish hello from postman to robot-market/test/v1/sim-001/telemetry, QoS 1, retain off.
Open http://127.0.0.1:8080/. It should appear as message_received with its raw contents.

The test broker no longer restricts topics by username. Any test account may also subscribe to that topic in Postman to receive its own publication. The browser watches all topics under robot-market/test/v1/# and applies no JSON, device-ID or timestamp validation. Your previous JSON payload, including a literal {{$isoTimestamp}}, is displayed as supplied.

TLS is also available at mqtts://109.122.252.129:8884 with the supplied private CA. If a Postman send does not appear, inspect the connection state and publish acknowledgement. The Go simulator is not needed.

Receive the backend's application ACK

In Topics, subscribe to robot-market/test/v1/sim-001/acks before publishing to robot-market/test/v1/sim-001/telemetry. Every live test payload gets a JSON receipt_ack reply with ok=true, source topic, observed time, byte count and SHA-256. Optional message_id/request_id are echoed; they are not required. For ESP32's own topic path, subscribe to robot-market/test/v1/esp32-lab-001/acks. The UI shows receipt_ack_sent and outbound publication events. This is separate from MQTT PUBACK.