Want to connect to Fibaro-switch via IUNGO energy meter

App version: latest
Phone OS: Android
Problem description:

I have an IUNGO energy metering system - I can program a switch to ON/OF.
I tried this with an API-tester (Talend API tester) - works like a charm.
I want to do the same with Olisto using a button so I configured the following:

POST
http://192.168.178.111/iungo/api_request

BODY (JSON) for off:
{“method”:“object_prop_set”,“arguments”:{“oid”:“7f517ae8”,“prop”:“command”,“value”:“off”}}

BODY (JSON) for on:
{“method”:“object_prop_set”,“arguments”:{“oid”:“7f517ae8”,“prop”:“command”,“value”:“on”}}

What could be the issue?

Thanks!