Found this: here : https://audi.tolltickets.com/fr/faq/
If your windscreen is fully coated or if you are unsure whether it is, we can only recommend that you hold the toll box out of the side window when you come to the toll station.
The toll box must already be held out of the side window when approaching the toll station (approx. 100 m in advance).
This is important so that the antenna signal of the toll station can activate the device from sleep mode. Please orientate the toll box so that the holder faces forward towards the toll station. Please do not wave with the toll box.
It is indeed often the case that some models of the vehicle manufacturers Porsche, BMW, Mercedes, Audi, Tesla etc. and usually some electric vehicles have fully coated windscreens without recesses of the coating. In these cases, the device must indeed always be held out of the window when approaching the toll station.
Unfortunately, we have no influence on this fact, as the funtioning of the toll boxes is determined by the toll operators.
Manufacturers of vehicles sold in Germany often do not include a recess for toll devices due to the non-existent passenger car toll in Germany.