Troubleshooting
Your FASTag did not scan
The barrier stayed down and the queue behind you did not care why. There are only a handful of reasons a tag fails to read, and you can rule out most of them from the driver's seat.
1. Placement
The tag belongs inside the windscreen, at top centre, flat against the glass. A tag on the dashboard, held up by hand, or stuck to the outside will read unreliably or not at all.
2. Windscreen film
Metallic or heavily tinted film blocks the radio field the plaza aerial relies on. This is the cause people almost never suspect, and it is common on vehicles fitted with aftermarket sun film. If the tag worked before the film went on, that is your answer.
3. Balance
A short balance is the single most frequent failure. Keep a buffer well above one crossing, because the deduction and the reading happen in the same second and a marginal balance fails in ways that look like a hardware fault.
4. Status
The tag may be blocked or blacklisted for reasons unrelated to balance — incomplete KYC, a duplicate tag against the same vehicle, or a registration mismatch.
A failed crossing generally leaves a short window — around 72 hours — to settle before it is recorded as an unpaid due against the vehicle. Unpaid dues follow the vehicle, not the driver, so they surface when you sell it.
Physical damage
A tag that has been peeled off and re-stuck, creased, or cleaned with solvent may have a damaged aerial. Tags are not designed to be removed, and a damaged one needs replacing rather than repositioning.