Problem posting acknowledgement to RN Partner

I using webMethods for Rosettanet 4.6 to receive 7B1 PIP from one of my partners which is using Inovis(Extricity) at their end to send the PIP document. We have the proper conversation etc. taking place in our webmethods software, but are facing a problem.
The acknowledgement we send to them upon receipt of the 7B1 shows as having beeen sent properly to the https URL with a response code of 202 in the logs. But the partner is not receving the ack. and the software at their end keeps retrying 3 times as per the RNIF 2.0 settings. Could anyone, who has faced a similar problem or with some idea about the Inovis product help me out with this.

Thanks in advance,