I have had no luck getting the above method to work, but have started using the new rpc API and it is working as expected with the following example commands.
Shelly | Shelly Technical Documentation
This service is common for all Shelly-NG devices. It handles device management.
shelly-api-docs.shelly.cloud
Code
curl -X POST -d '{"id":1, "src":"user_1", "method":"Shelly.ListMethods"}' http://${SHELLY}/rpc
curl -X POST -d '{"id":1, "src":"user_1", "method":"Switch.GetStatus", "params":{"id":0}}' http://${SHELLY}/rpc
So it's a case or RT*M - but it has to be the right version.
Unless anyone can post to tell me what I was doing wrong with the first post and the basic HTTP interface?