Hey there.
You should be able to check the web.log of your instance for an error message (it may help to turn the logging in global Administration > System > Log Level up to DEBUG) and trying to validate your configuration once more.
If you see an error like PKIX path building failed – it is definitely the result of using a self-signed certificate. Often, when a self-signed certificate is used, the truststore that Java uses (which runs your SonarQube instance) can’t trust that certificate. Adjusting the truststore to add the certificate and restarting your SonarQube server will resolve the issue.
You may see another error like Hostname not verified which requires other actions.
In any case – start looking at the logs and see what they tell you 