When using an iPhone 5, you should have a valid SIM card to conduct transactions. For more information on installing/replacing a SIM card, refer to the appropriate Apple documentation or visit the Apple Web site.
If the terminal shows an exclamation at the top bar, this means that the terminal holds data that it failed to synchronise with the Adyen platform due to lack of an outgoing internet connection.
The two Action buttons located on both sides of the terminal, activates the barcode reader. Press either of the buttons to scan barcodes.