Connect-Rest error : SSLPeerUnverifiedException: Certificate for <x.x.x.x> doesn't match any of the subject alternative names
Test connectivity from Pega to Connect-Rest service is Fail with below error:
com.pega.pegarules.pub.services.ConnectorException: Caught unhandled exception: java.lang.RuntimeException: javax.net.ssl.SSLPeerUnverifiedException: Certificate for <x.x.x.x> doesn't match any of the subject alternative names: 
The Test connectivity is working fine initially. But the certificate got expired. After installing the New certificate this issue is observed.
Is there any way to resolve this issue from Pega or what details do we need to ask Service provider?
Your first action should be verifying if the certificate is valid or not, outside Pega, using 3rd party tools like Postman or SoapUI. If not working, then this is a generic issue, which likely the case based on your description. Otherwise, check the Pega side how the certificate is applied, at JVM level/app server or connector level and act accordingly to update the new certificate.