Usually the arrangement is the following: Rental cars are equipped with a toll transponder device, upon collection of a rental car you'll be asked for a 20 euro cash deposit for the transponder.

This includes 15 Euro worth of pre-loaded credit and enables clients to use the toll road without having to visit local pay stations/post offices for payments.

An option to add more credit (by a minimum of 10 euro and multiples hereof) to the transponder is available upon collection or during the rental.

Remaining unused toll will not be refunded.

If you know in advance that you'll not use the A22 the 20 euro cash deposit, will be replaced by a credit card slip which will be kept for 5 days after the return of the car then destroyed.

Most of the rental companies in Faro Airport Car Park 4 (P4) take 20 euro cash deposit, should the A22 (or any other motorway in Portugal) not be used they will refund the 20 euro either in cash or by credit card credit, the latter takes a few weeks.