Hi Swanashree,
There might be multiple reasons for this problem. Network connectivity, problem in receiver server port etc. Things you can check
1. Telnet/Ping target server from client network , check if the request is able to reach the target server.
2. There may be problems in receiver server accepting the payload from PI. This they need to check from their end.
3. Try XPI inspector. For details check this wonderful blog by Michal Krawczyk
Michal's PI tips: XPI inspector - help OSS and yourself
Regards
Anupam