Tristan Fewings/Getty Images for Apple

Transport for London has warned people using Apple Pay on London's transport network to use the system properly or risk being overcharged for their journey.

People touching in with an Apple Watch and out with an iPhone linked to the same Apple Pay account are being charged a maximum fare. This issue, which TfL describes as "card clash" is a result of how Apple Pay works.


The service, which launched earlier this week, has caused some confusion among early adopters. Apple Pay "creates its own unique ID for each product", a TfL spokesperson told WIRED.co.uk. This is actually to enhance security: Apple devices do not retain your credit or debit card numbers, but record a unique, encrypted device account number, on a dedicated chip, every time you add a card to an Apple Watch, iPhone or iPad.

In this way, Apple ensures that anyone with unauthorised access to your device can't retrieve your actual bank account information.

However, that by definition means an iPhone and Apple Watch linked to the same bank account will have separate IDs, and count as two separate travellers on TfL services. People are advised to only use one device when travelling around London.

We asked TfL how its weekly caps would work on the system. Specifically, WIRED.co.uk asked if two Apple devices, each using the same Apple Pay account, would contribute to a single weekly cap on charges, or if two running totals would be kept. TfL explained that all charging and capping was done on "the basis of individual devices". "To benefit from daily and weekly capping customers need to use the same device. Data on which devices are paired with each other is not available to us," the spokesperson explained. "If two devices linked to the same account are used on the same day they will get billed twice."


If people try to trick the system by sharing Apple Pay devices with friends or relatives, TfL said its fraud prevention algorithms would pick up on unusual activity.

Apple Pay could also cause problems if the device used to touch in runs out of battery during a journey. This would prevent people from being able to touch out, resulting in the maximum fare being charged.

Early adopters have also complained about the speed of Apple Pay compared to Oyster or contactless. Difficulties using Touch ID to authenticate payments combined with the speed at which a payment is recognised have been causing problems for some.