docs: function (context_uid, sender, receiver, channel, message, meta) {
          if (!this.api_key) throw new ChangeTipException(300);
          if (!channel) throw new ChangeTipException(301);
  
          var deferred = Q.defer(),
              data;
  
          data = {
              context_uid: context_uid,
              sender: sender,
              receiver: receiver,
              channel: channel,
              message: message,
              meta: meta
          };
  
          this._send_request(data, 'tips', null, Methods.POST, deferred);
          return deferred.promise;
      }