To make a long story short, on Android 4, Google blocked self-signature implementations, which we had used to code our app, so in turn, Sesame couldn't connect to our servers. The main issue preventing you from accessing Sesame is most likely being unable to connect to our servers, which we had cut off because of unreliability.
Since most of our users are using Android 5 and above at this point, the server aspect can be fixed any time, so what we need to do next is to test for bluetooth stability and connectivity on Android 4. If all goes well, we should be able to support users of Android 4.x soon. I'll try to follow up on the progress of this. Do remind me if I don't give an update.