REST API Patch issue...

The HTTP verb you use will determine that. If I want to update existing properties, i use PUT. If i want to create a new one, i use POST.

These examples are for devices, but it's similar for groups:

To create a new property on device 43 called "my.new.property", I POST to "/device/devices/43/properties/" with the following payload:

{
    "name": "my.new.property",
    "value": "value of the property"
}

If i repeat the same action, i get this response:

{
    "errorMessage": "Property(name=my.new.property) already exists in device(id=43)",
    "errorCode": 1400,
    "errorDetail": null
}

So, to update that property with a new value, I do a PUT to "/device/devices/43/properties/my.new.property" with the following payload:

{"value":"Star Wars!"}

More reading: https://medium.com/backticks-tildes/restful-api-design-put-vs-patch-4a061aa3ed0b