My NFC card does not open anything

In order of frequency.

NFC is off on the phone. On Android it is a setting, and it is off on many phones by default. On iPhone it works from the iPhone 7 with the screen on and unlocked.

Wrong spot. Hold the card against the upper back of the phone, not the middle, and keep it still for a second.

A thick case, or a metal one. Metal blocks NFC entirely. Ask the person to hold the phone's edge out of its case.

The card is not activated. Check "My cards": if the code was never entered, the card points at nothing.

The card is disabled or assigned elsewhere. Same screen: check which card it points at.

Still nothing on two different phones? Write to us with the code printed on the packaging.