I have had trouble trying to get the set temp option into hassio but I had the working curl command so I have setup some bits in node red instead if it is any use to anyone.
[{"id":"37d01ae9.869d66","type":"change","z":"6414843e.b4e3dc","name":"Set Hottub 42C","rules":[{"t":"set","p":"headers","pt":"msg","to":"{\"Content-Type\":\"application/json\",\"Accept\":\"application/json\",\"X-Gizwits-User-token\":\"*********\",\"X-Gizwits-Application-Id\":\"***********\"}","tot":"json"},{"t":"set","p":"payload","pt":"msg","to":"{\"attrs\":{\"Temperature_setup\":42}}","tot":"json"}],"action":"","property":"","from":"","to":"","reg":false,"x":400,"y":140,"wires":[["dea77fd.b480f8"]]},{"id":"dea77fd.b480f8","type":"http request","z":"6414843e.b4e3dc","name":"","method":"POST","ret":"obj","paytoqs":"ignore","url":"https://api.gizwits.com/app/control/***********","tls":"","persist":false,"proxy":"","authType":"","x":590,"y":140,"wires":[["3dcdb20.e1f894e"]]}]
I can then easily automate the temps for me offpeak and onpeak tariffs.