For those in the UK who may have had a Liber-T motorway tag in the past and paid by credit card this has now been stopped due to some bureaucratic nonsense in France meaning all must now be settled by direct debit, so unless you have a French address and bank account, you're bang out of luck. However, SANEF, the company that run the northern French motorways have come up with an answer, they have started a UK subsidiary supplying tags to the Brits and billing monthly in GBP to your UK bank account, have a look at it here -
https://www.saneftolling.co.uk/supportI'm sure it was not written by a native French speaker as
section 6.2 is absolutely super and the French just don't understand humour at all
6.2. Is there an alternative to tolls?
Yes! There are free roads if you do not like smooth, high quality motorways and don’t mind arriving late for your ferry. The N138 is our favourite, but a section of that is shut in mid June so the Brits can race cars on it (Le Mans).