Paying for bus

I use and iPhone 7plus iOS 11.4.1 with a Barclays Bank Debit card in my wallet app. I use apple pay to pay for items at most shops with no issues.

However when I tried to board a London bus this morning 13.11.18 I used apple pay against the contactless bus reader which flashed with a red light and declined the payment unfortunately the apple pay app states that a payment has been made. I showed this to the bus driver to refused to accept a payment had been made.

I tried this again and the same thing happened. When I use the same actual debit card against the bus contactless reader I never have an issue. The light has always been green with a payment accepted.

How can you stop this from happening? I believe now the I will be charged twice by iTunes.