Error while sending message to SENDER REST Communication channel

hi,

    my scenario is :

     Webservice to Proxy. The sender system is a REST based system and is sending data in XML format to PI REST Adapter.

Error while sending the request payload to the PO server is as below :-

Error while sending message to module processor: Sender Channel 'RESTSenderAbc' (ID: b53185f6500a3a64a4e0a22ca37b51bf): Catching exception calling messaging system: Receiver Determination did not find any receivers at all: Receiver Determination did not find any receivers at all.

The URL we r using - https://abc1.xyz.net:51001/RESTAdapter/Abc/