Hi @arnaud.brun.vidal,

I discovered this thread by chance, after stumbling on {"single_api": true} myself.
I tried to apply your solution, but unfortunately, it doesn’t work for me: I get an error back (via an alert) saying that listProperties is not a function.

This happens in the case I try the method on the list of things but it actually works if I do it on a single thing.

In my case this works fine:

const things = properties.things.get(0, properties.things.length());
const thing = thing[0];

return {
    return_value: JSON.stringify(thing.listProperties())
}

To see what is there, simply display the result into an alert.