How to charge a particular card on a customer with Stripe.com - ruby-on-rails

Question

A customer object can have many cards in Stripe.com. How do you charge an existing card?
I've tried a few things, but the stripe api for some reason borks when to get an old customer token and a new card token instead of just creating a new card on that customer. So I've gone the route of retrieving all the customer's cards, then selecting one by radio button, then submitting the token of the chosen card into a charge
charge = Stripe::Charge.create(
:amount => "#{#subscription.price}",
:currency => "usd",
:card => params[:existing_card_id],
:description => "Subscription for #{current_user.email}"
)
but I get the error
Stripe::InvalidRequestError: Invalid token id: card_24j3i2390s9df

Answer 1

I figured this out.
With existing card tokens you have to send in the customer token as well
charge = Stripe::Charge.create(
:amount => "#{#subscription.price}",
:currency => "usd",
:customer => current_user.stripe_customer_id,
:card => params[:existing_card_id],
:description => "Subscription for #{current_user.email}"
)

Answer 2

This answer help to ME apply the same solution in PHP for charge an specific credit card customer, other than the default credit card. Here the pieces:
JSON:
{
"charge": {
"amount":122,
"currency":"usd",
"customer":"cus_7hVsgytCc79BL7",
"card":"card_17SENFJ4sx1xVfmD8skoSjNs"
}
}
PHP
$item = $params->request->getJsonRawBody();
$new_charge = \Stripe\Charge::create(array(
"amount" => $this->ConvertAmount($item->charge->amount),
"currency" => $item->charge->currency,
"customer" => $item->charge->customer,
"card" => $item->charge->card
));
return $new_charge;