Hi Kalyan,
Hypertext Transfer Protocol -- HTTP/1.1
https://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html
10.5.4 503 Service Unavailable
The server is currently unable to handle the request due to a temporary overloading or maintenance of the server. The implication is that this is a temporary condition which will be alleviated after some delay. If known, the length of the delay MAY be indicated in a Retry-After header. If no Retry-After is given, the client SHOULD handle the response as it would for a 500 response.
Note: The existence of the 503 status code does not imply that a
server must use it when becoming overloaded. Some servers may wish
to simply refuse the connection.
You are having a problem in your server (Error 500 are server errors) please review your SystemOut.log or share to give more support.
Hope this helps. Tell us if you need more support
Regards