You need to create and use ssl certificates for both domains ( mydomain.io, home.mydomain.io ).
Enter your domains at SSL Server Test (Powered by Qualys SSL Labs) . An analysis of your ssl setup will be done and all known issues like outdated ciphers, known vulnerable implementations of TLS/SSL etc. will be detected and reported.
Based on the report you can take actions and redo the test.
Uploaded my configuration at