Change payment method on existing subscription

If the user wants to change the payment method for the subscription, this can be done in three ways:

• Let the user choose between an existing payment method.
• Allow the user to enter a new payment method on a dedicated page, as described above for signing up existing users.
• Direct the user to a hosted page at Billwerk+.

The subscription object provides a link to a page:

"hosted_page_links": {
  "payment_info": "https://subdomain.reepay.com/paymentinfo/myaccount/4bc5f5f5536146a8b745aeab555162df"
},

The page provides a simple card entering page for changing card on subscription.