Make sure that the card has a contactless payment feature(marked with an icon)
Make sure the NFC model is turned on on the device.
Make sure that the card is touched to the location of the NFC module of your device. For more information, go to the App “tapXphone” User Guide > Payment acceptance.
Perhaps the case on your device blocks the signal of your NFC antenna, so remove it and repeat the operation
Make sure that the card is not removed from the field of reading of the NFC module too quickly.
Perhaps the antenna of the card itself is damaged (this is not a rare case, so you can check with the client how their card works on other payment terminals)
The NFC module may be damaged. You can try installing a third-party application designed to read NFC tags (for example, like this), and test the operation of your NFC with the help this application.