Got it to work finally, thanks.
See https://codepen.io/Jeoff75/pen/MLvYzm
I understood that mrbdrm talked about the dmx-text attribute and not regular html attribute.
But this is not obvious to find as the GUI says “Inner Text” so I couldn’t immediatly make the connection 
And this is “App connect” code I think.
I couldn’t locate a proper App Connect extensive documentation.
Do you know where I can find one ?