Why insecure connection on android?

Question

linux

SSL is installed and https on the PC works fine, on androids an insecure connection error pops up. with what can be connected?

Answer 1

For example, because the browser that you use on android does not have a CA certificate installed that issued your ssl certificate to
you, can you explain in more detail what exactly is the error, what is written there?

Answer 2

Perhaps the certificate on the server is installed incorrectly (for example, there is no chain in the certificate to the required CAs) or, as answered above, the CA / is not installed

Answer 3

Check your domain here https://www.ssllabs.com/ssltest/analyze.html
You will be given detailed information about your certificate and higher ones, as well as indicating any problems.
The most likely problem is that mobile browsers do not have the parent certificate in their trust store, in which case configure your server to issue both your certificate and the parent