rado It can be a pain sometimes. Key to acc, then click on the connect arrows in tunerpro, bottom will say connecting, then start the car, if it works it will say connected down the bottom and data will start flowing. Sometimes it don't work. Car off, acc, click connect, then start car usually works the 2nd time.
This assumes your cable is configured right and working.
It's really great what the smart people like Aaron have achieved with tunerpro and motronic, but they system is janky af. In time I'll haltech my 850 as tunerpro while great, gives me the shits at times.