Coap.getResponsePayload()
DESCRIPTION
Get response payload
DECLARATION
byte[] getResponsePayload()
THROWS EXCEPTIONS
NabtoRuntimeException:- with error code 
NO_DATAif the response does not include a content format. NabtoRuntimeException:- with error code 
INVALID_STATEif the response is not available. 
RETURNS
The payload. If the response has no payload, the empty buffer is returned.