If you card machine (payment terminal, credit card machine, chip and pin device etc) has a problem, you should contact the company that provided it. Tengo do not provide card machines directly, you will have a contect with a third-party supplier. If you have a supported, integrated card machine, the only thing that can affect functionality on our side is the configuration. There is a guide to entering the settings on yout till/EPoS unit in tengoPOS here. The only issue there can ever be from our side, is incorrect details being entered for the device you are trying to use.
Also, our software can run offline, but card machines cannot process transactions offline, so if you’re struggling to make sales with your card machine, you should also check your internet connection.