spotted this on FCC

Note: Some PAYG customers using FCC services to make journeys on these
'additional' PAYG routes will not be able to correctly 'touch in' or
'touch out' due to some FCC stations within the London Travelcard area
not having Oyster validators.

To prevent PAYG customers being charged for an incomplete journey in
these instances, the Oyster system will be set up to automatically
complete any journey starting or ending at a Zone 1 station where the
customer touches in/out. The charge made will be based on a journey
between the customer’s 'usual' start/finish station and the Zone 1
station where they touched in/out:

e.g. a PAYG customer who normally travels to/from Hendon Central to St
Pancras International will be charged for a PAYG journey from Hendon
Central to/from Zone 1.

Important note: this automatic completion process does not always work
and PAYG customers are advised that they may incur an incomplete
charge of £4 or £5. TfL are planning automatic refunds of any
incomplete charges incurred in Zone 1 on the days of industrial
action. If you have a query about the amount you have been charged or
you haven’t received an automatic refund within a week, please contact
the Oyster helpline on 0845 330 9876.


What if you don't have a "normal" journey?!