The service car stops need to be attached to the building (same way you did it with the remote bus stop). So that they can go to the service car stop and take the car to the assigned remote gate.
Actually you built service car stops next to the remote gates, you can remove them and place them direct at the building (same as your bus stops).
Build a door and make sure it’s marked as secure zone if you have placed them in the secure area.
To connect the gate to a service car stop, click on the gate. There is a button to connect the service car stop.
You can connect several gates to the same stop.