StartTransaction never acknowledged

How it presents

Symptom

StartTransaction never acknowledged — Authorize succeeded but StartTransaction.conf never returns; session hangs Preparing/Suspended. protocol field note: keep evidence scrubbed and prove the ranked cause before module RMA on OCPP-F04.

Root causes (by observed frequency)

1. #1 CSMS overload or filter dropping StartTransaction

   Authorize worked — path partially up

2. #2 ConnectorId mismatch vs CSMS configuration
3. #3 MeterValue/clock prerequisites failing CSMS validation
4. #4 Charger websocket half-open after NAT flap mid-start

Diagnostic procedure

1. 1. Trace Authorize OK then StartTransaction timeout in CSMS

   Expected: Where it stops

   Tools: CSMS logs

2. 2. Verify connectorId mapping for that gun

   Expected: Matches commissioning

   Tools: HMI/CSMS

3. 3. Check station time and meter registration health

   Expected: Sane clock/meter

   Tools: HMI

4. 4. Force clean reconnect; watch a single start attempt

   Expected: StartTransaction.conf

   Tools: CSMS

5. 5. Escalate to CSMS vendor if charger traces show send without conf

   Tools: both vendors

The fix

StartTransaction ack failures are CSMS/config/websocket — not DC modules.

1. Confirm Authorize is healthy before chasing StartTransaction.
2. Correct connectorId and meter configuration mismatches.
3. Stabilize the websocket (NAT/keepalive) around session start.
4. Retry with a clean Boot/reconnect only after config is verified.
5. Open a joint ticket with CSMS if conf never returns on a clean path.