It is possible to vault (store) a card or any other payment method that supports vaulting by setting the store field in the request body to true. 
curl -i -X POST "https://api.example.gr4vy.app/transactions" \
    -H "Authorization: Bearer [JWT_TOKEN]" \
    -H "Content-Type: application/json" \
    -d '{
          "amount": 1299,
          "currency": "AUD",
          "store": true
          "payment_method": {
            "method": "card",
            "number": "4111111111111111",
            "expiration_date": "11/25",
            "security_code": "123"
          }
        }'
This eliminates the need to separately vault the payment method and then use it to create a transaction.
Learn more about payment method vaulting as well as linking payment methods to registered buyers.
Storing a redirect payment method requires us to redirect the user only once. This would vault the payment method and process the transaction.