After I activated my Lorawan gateway this afternoon, it is now clear it works! In my part of town a few sensors for the Measure Your City network have been installed (one in my garden but currently offline after a storm knocked it out of the tree). Those sensors are now picked up by my gateway and the Measure Your City database shows my gateway as the path along which the data was collected.

One of the sensors (number 105), located two streets away from our house, is now using my gateway to log its data to the central Measure your city database.