[San Francisco] Bay Area Rapid Transit (BART) requires that you get into the paid area in order to pay for parking. So if you forgot to pay for parking and ask a friend or family member who is not riding on BART to go help you pay for parking for you, they will not be let into the paid area to pay for parking.
In particular the Walnut Creek BART station has the parking payment machines 30 feet inside the turnstiles. The three attendants in the morning will not let you in to pay parking and will not take your money to pay for the parking. The three attendents will just talk to each other and one will answer and tell you how they will not do anything and will not help in any way.
You have to ask someone who is going into ride BART [give them the money] to pay for the parking, otherwise you will have to pay $8.50 in addition to paying the $3.00 for parking.