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The server is also not aware of the newly created truststore. Therefore, import the Jira cert into the servers truststore.
Troubleshooting
Test that you get an OK connection using SSLPoke from Atlassian https://confluence.atlassian.com/kb/unable-to-connect-to-ssl-services-due-to-pkix-path-building-failed-error-779355358.html
Verify the cert is in the truststore
Go to Logging and profiling add a new log se.rixter with DEBUG as log level, execute an iHub action and check the logs.
Guide for SSL cert imports
https://www.sslshopper.com/article-most-common-java-keytool-keystore-commands.html