Tradfri binding - lost

I’m lost on the Tradfri binding

Since the disconnection / communication errors with the TradFri hub started a while ago, I’ve left the system disconnected from OpenHab.
Today, I found some threads indicating that it works again so I gave it a try. Not all topics clearly state what openhab versions people are using and whether they use paperui or config files, which makes it hard to debug

I’m on openhab 2.4 and use config files to define all things / items

After a few tries I gave up.
Using paperui it seems to work. The gateway connects (at least once, did not spend enough time on it to see if it disconnects again)
Using config files I do not get it to work since I cant find the pre-shared key anywhere.

Does anybody know if&how to get the Tradfri binding/hub working using text files.

Thank you

Have a look here. Tradfri 1.8.25 - offline - communication_error

I use config files. 2.5m1. I suggest this version over 2.4.