Hi Marios, in your first REST call, not sure if its complete, but you seem to be updating only histogram1 property as your REST call is only setting /Sensor001/Properties/histogram1 i think this is why you also get error when you only try to update hsitogram0 with that call. Did you try switching it to "*"
Something like .../Sensor001/Properties/*
What exact error do you receive for 2nd REST call? Could suggest to use Postman to formulate right REST calls, makes debugging easier
Not sure if you have already seen this, but there are some nice explanation and examples in this blog REST API Overview and Examples