Illegal character ((CTRL-CHAR, code 31)) Error in POST API call

Summary

Calling REST API to create custom child record of opportunity

Content

https://INSTANCE_URL:443/crmRestApi/resources/latest/opportunities/##OptyNum##/child/TradeInEquipmentsCollection_c

The above one is the REST API URL which created in web service connection. Below is the Request Payload of the API,

{"AssetDCL_Id_c": 300000323440088,"Opportunity_Id_c": 300004145009227}

While calling the API from before update trigger of Asset object getting an error as 

Exception in expression "oracle.apps.crmCommon.assetImport.publicModel.entity.AssetEO" trigger "AssetCheck" : oracle.binding.expr.ServiceInvocationException Unexpected exception caught: org.codehaus.jackson.JsonParseException, msg=Illegal character ((CTRL-CHAR, code 31)): only regular white space (\r, \n, \t) is allowed between tokens at [Source: weblogic.net.http.KeepAliveStream@7feb72ea; line: 1, column: 2]: Illegal character ((CTRL-CHAR, code 31)): only regular white space (\r, \n, \t) is allowed between tokens at [Source: weblogic.net.http.KeepAliveStream@7feb72ea; line: 1, column: 2]