Microgateway Rest API POST JSON message body missing - DFHWrapper error

[sushobhanmonda1]

I'm using Apigee Microgateway (2.5.12) to call a backend unsecured CICS application. I'm making a POST request with a valid JSON and using only oauth plugin. I'm passing below headers with my request:

x-api-key <key> 
Content-Type application/json 
Accept application/json 

I'm receiving below error:

{
    "Fault": {
        "faultstring": "Failure interacting with CICS",
        "detail": {
            "CICSFault": "Failure to parse JSON request for WEBSERVICE <svcName> and HTTP Method POST: Error obtaining parser from data source:Missing value. at character 13 of {DFHWrapper: }"
        }
    }
} 

It looks like the JSON message body is not being forwarded by Apigee to CICS. I've tried from Postman and SoapUI, have validated that the JSON is valid, have confirmed that all headers are set correctly, have verified that the CICS API works when invoked directly (without through Apigee).

Any idea what might be causing this error? Are any additional settings required in Edge or MGW to allow JSON to pass? Is there a way to capture the outgoing message from MGW or Edge?