Creating a snapshot via the api is unfortunately very hard to use externally. The problem is that the snapshot data is saved in the dashboard json on the Grafana frontend and then the dashboard json with the embedded snapshot data is sent to the api. Basically, you need the Grafana frontend to generate a snapshot. The API just saves the result.
It is on our TODO list to make a better API for snapshotting that uses headless chrome to be able to do a server side render of a panel.
