@brainstimulationab What you are trying to achieve is not doable at the moment. You have to be logged in to the Flic app in order to pair a button the first time. This means that for the button grabber to work you have to be logged into the Flic app once the "Grabbing" occurs. I know that some people, like you, feel that this is not very optimal when building an app that is centered around the Flic button, but that is how the situation is at the moment.
The idea from our point of view was from the beginning to allow the "grabbing" of the button to other apps in order to extend the functionality for our users. But I do realize that it can be a bit confusing for users coming from the other way around.
