Retrieve credit card token from Payment Method

I have to save my users' credit cards using stripe for flutter.

I currently use the "stripe_payment" plugin and using the StripePayment.addSource() method I enter my credit card details and retrieve the payment method token.

To add a customer and card on stripe I need a credit card type token.

stripe.customers.create({
    source: user_card_token,
    email: user_email
})

How do I recover it having only the payment method using the node stripe API?

Alternatively, is there a more comprehensive plugin?