In this example ,I change the server to my vps ip.
I have closed the firewall in server machine.
I run the b4j client ,they work very well.I can get the messge in server.
But I insrtalled the B4a client in my phone ,I can get nothing.
I have spend lots of time ,check the vps, the code.
But I think your idea is more useful.
After all i am too new to B4X.Learn new things is not easy.
I just changed this "uses-sdk android:minSdkVersion="15" "to "uses-sdk android:minSdkVersion="16""
SOLVED!
I donn't know why!
I just try this ,I see somewhere ...