My mum used the Dartford crossing back in August 2015 and paid the charge prior to her crossing. At the time she paid the charge, the online form didn’t have the recently added “Find vehicle” button, so she entered what she thought was her number plate, but made one small character mistake.
Roll on December 2015 and she received a penalty notice! Rather flustered about having to pay a fine charge on top of the payment she’d already made, I phoned the number and found out that since it was the first offence, you could simply pay the “missed” payment amount.
What was wrong with the online form at the time was that there wasn’t an option to check that the number plate you’d entered was valid. A rather simple addition… but it must have made the govenment quite a bit of money in fines!
It’s good to see this has now been changed and there’s a “Find vehicle” button which searches for the vehicle description.
What it does show though is that if there’s an API available to display more information about user entered data – in this case DVLA lookup – consider providing this as a feature to your users to prevent mistakes.