Reproduce:

• Finish an external task with POST failure and add errorDetails as JSON to the payload.
• Call GET engine-rest/external-task/ {id} > errorDetails is null
• Call GET engine/external-task/{id}/errorDetails > errorDetails are returned

Cause:

• ExternalTaskQuery does not fetch errorDetails from ByteArray table by default. But GetExternalTaskErrorDetailsCmd does.
  • https://github.com/camunda/camunda-bpm-platform/blob/master/engine/src/main/java/org/camunda/bpm/engine/impl/persistence/entity/ExternalTaskEntity.java#L276-L278
  • https://github.com/camunda/camunda-bpm-platform/blob/master/engine/src/main/java/org/camunda/bpm/engine/impl/cmd/GetExternalTaskErrorDetailsCmd.java#L54

Solution:

• Remove errorDetails from ExternalTaskDto
• Document /external-task/ {id}/errorDetails