If a workflow has a webhook input action, you can start it with this API. See the documentation in the workflow editor for details
/api/v2/workflow/{workflow_id}/node/{node_id}/start
The GUID of a wokflow
00000000-0000-0000-0000-000000000000
The GUID of a wokflow
00000000-0000-0000-0000-000000000000