Since I use for some time Runtastic Pro as a running app, I did not have to download the app. Thus I have the activation code for the app at first paid no attention. A connection lies not manufacture itself. After a long search, I noticed that the Runtastic chest strap looks exactly as the PM250. This must be enabled on the Runtastic website. In my distress I have the activation code for the app (!!) there so registered as it was printed on the enclosed Zellel - with dashes. The page showed me to a faulty code. When I then omitting the hyphen, worked because the code and see, suddenly the belt with the iPhone has connected. I hope this helps other buyers in a desperate search for help for the connection problems.