Very Good Peter,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.
Working Online and Offline is the good way for apps.
Which library do you use for Barcode reading, and please which bluetooth device did you get, I'm looking for such solution for our in house app.
Internal use of the mobile Apn is not very good, neither very speed for barcodes