Bad request when invoking rest api through OIC gen3

Summary:

I am trying to invoke a rest api through OIC gen3, it is giving "400 Bad request, There was a validation error."

I am passing 90+ fields in the request as per the design, somehow it is working with a few 5-7 fields in request whereas failing when passing all fields.
Whereas the same request (copied from OIC activity stream), is working fine from postman and giving results.

Content (please ensure you mask any confidential information):

{
"type" : "http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.5.1",
"title" : "Internal Server Error",
"detail" : "",
"o:errorCode" : "",
"o:errorDetails" : [ {
"type" : "http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.4.1",