Get the response data.
The payload is available until nabto_client_coap_free is called.
NABTO_CLIENT_DECL_PREFIX NabtoClientError NABTO_CLIENT_API nabto_client_coap_get_response_payload(NabtoClientCoap* coap, void** payload, size_t* payloadLength)
NABTO_CLIENT_EC_OK if a payload exists and payload and payloadLength is set appropriately. NABTO_CLIENT_EC_NO_DATA if the response does not have a payload NABTO_CLIENT_EC_INVALID_STATE if no response is ready yet.