flowable/flowable-engine · error · FlowableIllegalArgumentException

Invalid action: '

Error message

Invalid action: '

What it means

executeTaskAction dispatches only on the known actions: claim, complete, delegate, resolve. Any other value in TaskActionRequest.action falls through to a FlowableIllegalArgumentException whose message embeds the offending action string (the bracketed message is the prefix before interpolation).

Solutions

1. Use one of the supported action strings: claim, complete, delegate, resolve (all lowercase)
2. Normalize/validate the action client-side before sending
3. Check the ActionRequest constants (TaskActionRequest.ACTION_*) for the exact values supported by your Flowable version

Example fix

// before
{"action":"completeTask"}
// after
{"action":"complete"}

const SUPPORTED_ACTIONS = ['claim','complete','delegate','resolve'];
function assertValidAction(action) {
  if (!SUPPORTED_ACTIONS.includes(action)) {
    throw new Error(`Unsupported action '${action}'; use one of ${SUPPORTED_ACTIONS.join(', ')}`);
  }
}

function isTaskAction(s) {
  return ['claim','complete','delegate','resolve'].includes(s);
}

try {
  await post(`/cmmn-runtime/tasks/${taskId}`, { action });
} catch (e) {
  if (e.status === 400 && /Invalid action/.test(e.body.message)) {
    throw new Error(`'${action}' is not a supported CMMN task action`);
  }
  throw e;
}

When it happens

Trigger: POST /cmmn-runtime/tasks/{taskId} with {"action":"finish"}, {"action":"CLAIM"} (case-sensitive mismatch), a typo, or an action name valid only in the BPMN REST API.

Common situations: Case-sensitivity mistakes ('Claim' vs 'claim'); reusing action names from a different API; free-form UI input passed through without validation; new actions assumed to exist in this Flowable version.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

• A request body was expected when executing a task action.
• Illegal action: ' '.
• Invalid action: ' '.
• Unsupported variable query operation
• Unsupported variable query operation: " +…

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/15187ae8a34e6728. Report an issue: GitHub.

Appendix: source

Thrown at modules/flowable-cmmn-rest/src/main/java/org/flowable/cmmn/rest/service/api/runtime/task/TaskResource.java:138

        }

        if (TaskActionRequest.ACTION_COMPLETE.equals(actionRequest.getAction())) {
            completeTask(task, actionRequest);

        } else if (TaskActionRequest.ACTION_CLAIM.equals(actionRequest.getAction())) {
            claimTask(task, actionRequest);

        } else if (TaskActionRequest.ACTION_UNCLAIM.equals(actionRequest.getAction())) {
            unclaimTask(task);

        } else if (TaskActionRequest.ACTION_DELEGATE.equals(actionRequest.getAction())) {
            delegateTask(task, actionRequest);

        } else if (TaskActionRequest.ACTION_RESOLVE.equals(actionRequest.getAction())) {
            resolveTask(task, actionRequest);

        } else {
            throw new FlowableIllegalArgumentException("Invalid action: '" + actionRequest.getAction() + "'.");
        }
    }

    @ApiOperation(value = "Delete a task", tags = { "Tasks" }, code = 204)
    @ApiImplicitParams({
            @ApiImplicitParam(name = "cascadeHistory", dataType = "string", value = "Whether or not to delete the HistoricTask instance when deleting the task (if applicable). If not provided, this value defaults to false.", paramType = "query"),
            @ApiImplicitParam(name = "deleteReason", dataType = "string", value = "Reason why the task is deleted. This value is ignored when cascadeHistory is true.", paramType = "query")
    })
    @ApiResponses(value = {
            @ApiResponse(code = 204, message = "Indicates the task was found and has been deleted. Response-body is intentionally empty."),
            @ApiResponse(code = 403, message = "Indicates the requested task cannot be deleted because it’s part of a workflow."),
            @ApiResponse(code = 404, message = "Indicates the requested task was not found.")
    })
    @DeleteMapping(value = "/cmmn-runtime/tasks/{taskId}")
    @ResponseStatus(HttpStatus.NO_CONTENT)
    public void deleteTask(@ApiParam(name = "taskId") @PathVariable String taskId, @ApiParam(hidden = true) @RequestParam(value = "cascadeHistory", required = false) Boolean cascadeHistory,
            @ApiParam(hidden = true) @RequestParam(value = "deleteReason", required = false) String deleteReason) {

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