code: public ListenableFuture<PaymentIncrementAck> incrementPayment(Coin size) throws ValueOutOfRangeException, IllegalStateException {
          return channelClient.incrementPayment(size, null, null);
      }
docs: Increments the total value which we pay the server.
  
  @param size How many satoshis to increment the payment by (note: not the new total).
  @throws ValueOutOfRangeException If the size is negative or would pay more than this channel's total value
  ({@link PaymentChannelClientConnection#state()}.getTotalValue())
  @throws IllegalStateException If the channel has been closed or is not yet open
  (see {@link PaymentChannelClientConnection#getChannelOpenFuture()} for the second)