My phone does not detect any tag
If nothing reads at all, the phone is the variable and your tags are innocent. Four checks isolate it: the setting, the case, the antenna position, and whether a second phone reads the same tag. Three of the four cost nothing.
Four checks
Is NFC enabled? On Android it is a toggle that can be off silently. This alone accounts for a large share of these reports.
Is anything on the back? Case, metal mount plate, cards in a wallet case, a grip with metal parts.
Where is the antenna? The coil is small and its position varies, so a phone held in the wrong place reads nothing.
Does another phone read the same tag? If it does, the tag is fine and the first phone is confirmed as the problem.
Run them in that order. Each is cheaper than the one after it, and the first two are free.
The case is the usual culprit
An ordinary plastic or silicone case costs a little distance and is usually fine.
A case with a metal plate for a magnetic mount stops reading outright. This is the single most common accessory fault, and the plate is often invisible inside the case.
A wallet case holding a contactless bank card puts a competing tag directly between the coil and everything else.
Take the case off entirely for the test rather than reasoning about it. Reasoning about cases wastes more time than removing them.
Sweep, do not tap
Move the phone slowly across the tag rather than tapping in one place. A read is not instantaneous, so a fast pass can cross the coil without staying long enough.
Use the largest tag you have while searching, because a big antenna is easier to intersect.
Take several seconds per pass and cover the whole back of the phone before concluding anything.
Tapping repeatedly in one spot is the least effective way to establish whether a phone reads at all.
If all four pass
If NFC is on, the case is off, you have swept the whole back with a large tag, and another phone reads that tag, then the phone has a genuine problem.
Restart it once. Some devices get into a state where the NFC service stops responding and comes back after a restart.
Check whether the failure started after a system update, which is a distinct symptom with its own investigation.
And check whether the phone has NFC hardware at all, which is worth confirming before assuming a fault. It is a short check and it saves a repair appointment.
Frequently asked questions
Could all my tags be faulty?
It is possible and unlikely. If a tag that reads on another phone fails here, the phone is the variable.
Does a screen protector matter?
No. The coil is on the back of the phone, so anything on the screen is irrelevant to tag reading.
Should I factory reset the phone?
Not as an early step. Try the four checks, then a restart, and treat a reset as a last resort with a backup taken first.
Why does it work for payment but not tags?
Payment and tag reading use different modes and different software paths, so one can work while the other does not.