Given that you can only top up an Oyster card from an online order as part of a journey, are you sure it isn’t simply the standard deduction for the ‘journey start’ being made? i.e. adding £5 and then taking the £2.40 from that as whatever the standard initial fare deduction from your local station is.
As an additional question, are you actually taking a journey when you tap the card to top it up?
