Unable to pass runtime parameters when triggering Microsoft Fabric Data Pipeline via REST API – defa

Hi NuwanAthukorala ,

Thanks for the detailed investigation and for sharing the repro steps your findings align with the current behavior of Microsoft Fabric Data Pipelines.
At this time, passing runtime parameters to Fabric Data Pipelines via the REST API is not supported, it’s a current platform limitation. Even though the API accepts the request and the pipeline run is created successfully. Fabric currently does not apply these parameters to the pipeline run execution.
Even though Fabric accepts the parameters block in the API call, the pipeline still uses default values inside the pipeline execution and UI monitoring.

To clarify the REST endpoint (POST /v1/workspaces/{workspaceId}/items/{pipelineId}/jobs/instances) is correct and does trigger the pipeline run.

Seeing the execution in Fabric Monitor confirms that authentication, permissions, and item type are valid.
However, runtime parameters provided in the request body are currently ignored, and Fabric always uses the design-time default values defined in the pipeline. While the API contract exposes a parameters payload, parameter binding is not yet implemented for Data Pipelines.
Regarding the intermittent 405 - Method Not Allowed responses, this is a known platform side behavior and can occur due to backend routing, regional rollout differences, throttling, or when triggering the same pipeline in quick succession. It is not related to the request payload or parameter format.

Short term Workaround, If you must pass runtime parameters in API calls today, use a notebook instead of a data pipeline, since notebook REST API supports parameters now (preview).Runtime parameter support for Data Pipelines via REST is a known gap, and enhancements are planned, though there is no public ETA at this time.

Hope this helps.
Chaithra E.