In message
-septe
mber.org, at 11:23:38 on Sun, 17 Jun 2018, Recliner
remarked:
I don't know if TfL will periodically "retry" the charge, or what
happens next, and what timescale the card's blacklisting by TfL will
wear off.

From:
https://tfl.gov.uk/fares-and-payments/contactless/my-card-doesn-t-work#on-this-page-4

Occasionally your card may be accepted by our card readers, but the payment
is subsequently declined by your card issuer. If this happens:

- It means that you have made a journey which you have not paid for

- You will not be able to use your card again to travel until the unpaid
fare has been paid

You will get a notification for unpaid fares when you sign in to your
contactless and Oyster account where you can make a payment to clear the
unpaid fare. Alternatively, you can call us on 0343 222 1234 (TfL call
charges) or contact your card issuer.

Once an unpaid fare has been cleared, you will be able to use your
contactless card, mobile or other contactless device to travel again after
30 minutes.

If you do not clear the unpaid fare through your account or by phone, we
will try to do so by sending requests to your card issuer.

Some banks will charge the account holder a fee every time they "bounce"
an incoming payment

I know someone who had that happen (for the same payment) there times a
day, until they'd added some funds. They did get the fees refunded when
they complained, though.

If the payment is successful, this could appear on your card issuer
statement up to 30 days after you travelled.

--
Roland Perry