When I want to pay someone back, do I have to stay with the recipient until the end of the transaction?

No. The payer and the money receiver only need to be close to each other so that they can scan the QR code with their device.

You can of course also pay back friends remotely or receive money from them easily:

• Via 'Contacts' under the 'Pay' button at the bottom of the main screen, you can pay back someone remotely
• Via the 'Receive' button, you can easily send out a payment request so that you can receive money owed to you remotely.