"Gift a Discarded Vehicle Card" is a function for registering cars that can start the game "from Episode 21 of Story Mode" or "from a 600 HP/B Class car" on your friend's Banapassport Card. You'll get one Discarded Vehicle Card when playing 60 times with one vehicle.
You can do so on the Wangan Terminal. Prepare a Banapassport Card that can gift a Discarded Vehicle Card and a Banapassport Card to gift it to. The instructions are: "Touch the Screen" > "Use the Banapassport Card" > "Gift a Discarded Vehicle Card."
You can't touch "Gift a Discarded Vehicle Card" for Banapassport Cards that don't have Discarded Vehicle Cards that can be gifted.
The following situations may apply when you can't gift a card:
・You touched the source Banapassport Card when gifting.
→Touch the destination Banapassport Card.
・You touched a card that already received a Discarded Vehicle Card.
→You can receive another Discarded Vehicle Card when you use the first one on the drive cabinet.
・It was a Banapassport Card where 100 cars were already registered.
→You can't gift to a Banapassport Card that has 100 cars registered.
No, you can't gift an already gifted Discarded Vehicle Card to another card.
Since you can gift Discarded Vehicle Cards to any Banapassport Card other than your own, you can use your own Discarded Vehicle Cards by gifting your cards back and forth with friends that play Maximum Tune 5.