@shuvamd4   Can you tell us what troubleshooting you carried out?  did you find  support article "Application stops working on invoking a SOAP service" SA-45683  

There are some other posts such as 'I am getting an Issue In Connect SOAP.' which may help you troubleshoot.

Could you provide the complete error message, including the 'Caused by' lines?  We need more of the log stack to see the issue. 

Do you see HTTP -503 ?  The error code HTTP -503 Service unavailable is related to server which is unable to handle the request from client. 

Please enable debug level loggers given at reference URL

Also, go through the link https://www.howtogeek.com/360903/what-is-a-503-service-unavailable-error-and-how-can-i-fix-it/

Perform the following local-change:  1. Remove the new endpoind to old and run the connector activity. 2. Switch back to new end point and save the connector rule.

I would recommend tracing the call from pega and in the tracer turning on soap messages.  This will show you the message Pega is sending and you can then compare that to the SOAP UI message to see what is different.

Can you run successfully through soap UI?  

Please try to hit the SOAP service via Soap UI or any other third party client.  Check for the detailed reason of failure.  Compare the request format of Soap UI and from PRPC application ,  You will get the soap request message  from the tracer , definitely you would find a difference in it that causing this error.

You could also trace the traffic using fiddler or network monitor tools.

Most probably it could be a firewall issue. Check if the similar ports are enable for both the servers.

This may need a more in-depth investigation and require a support ticket.  Please can you provide the Incident ID if you chose to log a ticket?  This will help us track the issue and solution.