Apple Pay double click not working

Apple's official support article is avaialble here:

Use Apple Pay for contactless payments on iPhone - Apple Support

As a frequently user of Apple Pay, here are a few issues that I encounter frequently:

1. Make sure that the case on the iPhone is a quality case from a major manufacturer, otherwise, it may be interfering with the NFC signal. Trying without the case can diagnose this.
2. Just because you see a contactless payment icon at checkout does not necessarily mean that the store actually accepts ApplePay. Therefore, when testing, make sure that the store does indeed specifically support Apple Pay.
3. Make sure that when double-pressing the side button, that the phone is both in very close proximity to the contactless icon on the reader while also being at an angle that will allow Face ID to function correctly.
4. In the past, I had to make sure to choose "Credit" (and not debit) at my major grocery store or ApplePay would fail silently (has since been resolved and now I can immediately use ApplePay prior to selecting anything).
5. Sometimes ApplePay doesn't work if either the store is having technical issues. It can unfortunately fail silently and you, nor the store employees have any idea why. Trying it again at a later date would however work.

Have you enabled double click on your daughter’s iPhone? Please follow this path,

iPhone > Settings > Wallet & Apple Pay > Double Click Side Button > enable, if it’s already on, momentarily disabled then turn on again.

You can avoid the lines by taking to Apple Support. I’ve a feeling that credit card usage may not be permitted for minors use in electronic wallets.

You can reach Apple Support by calling 1-800-MY-APPLE.

How old is your daughter? Is she part of an Apple Family Sharing group? If so, did the organizer add the cards?

You’re welcome!