Sorry
@AS2 and
@Beja I completely forgot to answer your questions
@AS2 I wrote a code module that does all the work for me. Basically when an invoice in the SQLite DB has synchronised to the online MySQL DB it is marked as Boolean = True in the SQLite DB (there is a Boolean column called 'Synchronised' in the main invoice table). This way the synchronise query knows not to re-synchronise that particular invoice to the main MySQL online database again.
@Beja I've looked at this option but I'm not 100% sure as yet, there are lots of payment options out there including Paypal, SagePay, WorldPay, Nochex and lots of other business to choose from. I have a company beta testing this app for me at the moment, but I still have to look into adding a mobile payment system. I have added Bluetooth Barcode scanning and soon I will also be adding a 58mm mobile Bluetooth receipt printer
http://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20150527031224&SearchText=58mm bluetooth printer. In theory I've written the printer code for an 80mm serial printer and scaled it down to fit a portable 58mm Bluetooth printer, I've just ordered a printer so when it turns up hopefully my code will work first time out.