Main payment card in BT Pay is the BT card you use to pay when you bring your phone to the POS, if you have chosen to pay with your unlocked phone.

If you have more than one card in BT Pay and want to pay with another card, after accessing the app choose the card you want and bring your phone close to the POS.

The same goes for paying by phone via Apple Pay. 😃

The first card chosen for enrolment in BT Pay is automatically set as the main payment card.

Afterwards, you can set any of your cards as your main payment card at any time during the time you use the app by tapping on the desired card and selecting the "Settings"⚙ from the Cards menu. Then simply activate the "Main card for payment".

That's all! 😎