Documentation Missing

[DanielWikman]

There is no documentation online based on what I can find on how to use
"SimpleSelect by URL". Neither is there on YouTube.

I have tried all rest calls that the pim uses for a "regular" attribute,
and a number of others without success.

What url should I point to, to get it working with an existing SimpleSelect attribute?

[karelVanGeerdeghom]

You should create your own custom api call. If I recall correctly you should return a JsonResponse with

{
    "options": {
        "key": "value",
        ...
    }
}

Then in your controller you just load the attribute and it's options you want.

[DanielWikman]

What about using an existing simpleselect, those already has an API, controller etc, right?

That is the example I would like to see, rather than re-inventing the wheel.

[karelVanGeerdeghom]

Depends entirely on what the key/values are that you want to return. In my use-case I needed to return custom reference data entities.
Though I did end up just putting event listeners on my entities and simple updating/creating the flagbit simple select options directly.