No, it’s impossible to make an Apple Pay payment without your approval. You have to place your iPhone at least 4 cm from the store’s payment terminal to be able to use Apple Pay. Then, place your finger on Touch ID to validate it.
On iPhone X with Face ID, to authorise a contactless payment (in-store), you must confirm your wish to pay by pressing the side button of your device twice. Next, identify yourself using Face ID before hovering your phone in front of the store’s payment terminal.
To authorise an in-app or online payment, you must confirm your intention to pay by pressing the side button on your phone twice. Next, identify yourself using FaceID.
If the Apple Pay transaction isn’t complete 60 seconds after pressing the side button, you’ll need to reconfirm your intention to pay by pressing the button twice, for a second time.
On Apple Watch, press the side button of your watch twice and place the watch screen within 4 cm of the payment terminal.