All of the info you need for refueling (including the fuel card PIN) can be found at Step 6 - Fuel Instructions under Your Trips when you log in to your account during your trip.
The fuel card should be kept inside the glove box of each car, but if you don't find it here it's worth double checking all the cubby holes and sun visors to see if it's been left elsewhere.
If you still can't find the fuel card, (or if you are having trouble using it), please pay for the fuel yourself and make sure you get a fully itemised receipt.
Submitting your fuel receipt for a refund/credit
Email a photo of the fuel receipt to email@example.com OR upload a photo using the button at Step 6 - Fuel Instructions in the mobile site.
Car Next Door will credit the full amount to your Car Next Door account (with no expiry) within 5 business days. If you need the money refunded directly to you instead, please let us know when you submit the receipt.