Promo codes, loyalty points and what actually comes off the fare
Where discounts apply, where they do not, and why a code sometimes will not attach.
Discounts are simple until they are not, and most confusion comes from not knowing the order in which things are applied.
The order
The fare is computed from the route first: distance, time, ride class, stops. Then a promo code comes off. Then loyalty points, if you are redeeming any. What you see before confirming is the number after all of that.
Why a code sometimes will not attach
Codes carry conditions. A code may be for a particular service, or may have expired, or may be single-use and already redeemed on your account. If a code does not apply, the reason is that one of those conditions was not met.
Topsy checks a code against what the fare engine will actually accept at the moment of quoting, rather than accepting it optimistically and rejecting it at booking. That is deliberate: a discount that appears and then vanishes at the payment screen is the worst version of this experience.
Recurring trips
Worth knowing if you book a series: a promo code applies to the first occurrence, not to every trip in the series. The remaining occurrences are priced without it.
This is not a trap, it is arithmetic, but it does mean the total for a twelve-trip series is not twelve times the discounted first fare. The series total is shown so you can see the real number.
Points
Loyalty points are a funding source rather than a permanent price change. They come off a specific trip and are spent when they do.
What discounts never do
They do not change the driver's earning. A promotion is Topsy's cost, not the driver's, and a discounted fare does not mean a discounted job. This is worth stating plainly, because on some platforms it has not been true, and drivers are right to ask.
Checking
The quote shows the fare and, where a discount applied, what it was before. If the number is not what you expected, that comparison is the first place to look.