I have seen here several discussion about how to trigger a 2013 list workflow using REST, but so far I cannot succeed in running a site workflow, which should be basically easier. My code:
https://mysite.sharepoint.com/mysite/_api/SP.WorkflowServices.WorkflowInstanceService.Current/StartWorkflow(subscriptionId='0fa223dc-898e-493e-b523-c89ba796688b')
returns a BadRequest. The subscriptionId is correct and the WF called is a site workflow without parameter.
What am I missing?