Openhab3 update thing config without mainUI

Hi all,
I’ve recently upgraded from an old v2.* to a fresh v3 on a raspberryPi using openhabian.

On my previous install I was changing the max brightness (config 12_1) of a fibaro RGBW using a rule that would use -

sendHttpPutRequest(“”, “application/json”, “{‘config_12_1’:100}”)

This no longer seems to work on the new v3 install. I know the rest api now uses authorisation, but I still don’t seem to be able to get it to work with the username:password@ at the start of the url and I have basic auth turned.

Also going into the api explorer in the developer tools and using the GET /things/{thingUID}/config/status I receive [ ] as the response body on every ‘thing’, not just the zwave ones.
When using PUT /things/{thingUID}/config I just seem to receive a 500 server error.

I’ve also tried doing this with a python script -
for thing in [thing for thing in things.all if thing.UID.toString() == “zwave:device:92c72e81ee:node2”]:
thing.configuration.put(“config_12_1”, 100)
But although this does update the value shown within the mainUI it doesn’t actually have any effect to the light output.

Changing the value in mainUI and saving the thing does work, but I need to be able to do this through a rule.

I have seen that someone has edited then recompiled the binding to created new a new channel for config parameters they need access too, but this is beyond my capabilities and surely not necessary for something that I had working on the old install of v2.

I’ve spent hours over the last few days trying to figure this and I can’t seem to get it to work. Any help would be massively appreciated!

If I am not mistaken it is the same question as in How to use the API EXPLORER to change a thing configuration