Message.ack constructor
Creates an ack Message with Processig Code of 00 00 04.
Implementation
factory Message.ack({required String terminalId, DateTime? dateTime}) {
final x = Message('0300');
final now = dateTime ?? DateTime.now().toLocal();
x.processCode = 0x000004;
x.dateTime = now;
x.posConditionCode = 0x14;
x.terminalId = terminalId;
return x;
}