When testing the App it was noticed that it works, but no data readings are passed to the backend. The error message is an SSLHandshakeException with reference to a version mismatch. The MQTT Broker in the backend enforced TLS 1.2, in the debugging of app page I noticed, that the MQTT Client only uses TLS 1.0 as "enabled Protocols".
A short research shows that the availability of TLS 1.2 for Android <= 4.4 seems to be a common problem: https://ankushg.com/posts/tls-1.2-on-android/
The following points must be checked for the solution:
- Is TLS 1.2 installed as a protocol on the fleet boards?
- Is the protocol enabled?
- Is the MQTT client compatible?
TLS 1.2 should work when using customized clients for http or mqtt.