The easy way to create subscriptions, are with the use of Quickpay Form, through the payment window. To change a regular one-time payment to be a subscription, you have to add two additional fields to the form in your payment window:
subscription
Remember to add the two values to the checksum, that is being calculated, and sent with the form. When you have created a subscription, you get an ID, that should be saved for future transactions from this customer.
Remember to enable subscriptions for your acquirers in the Quickpay-manager under Settings > Acquirers.
To withdraw money from a subscription, use the POST /subscriptions/{id}/recurring request from the Quickpay API. In addition to the subscription id in the path, you will have to add the amount and a unique order_id for this recurring request.
For example, lets say you got ID 1234 returned when you created the subscription, and you want to withdraw 1,- DKK (currency was specified when you created the subscription and can not be changed in your recurring calls). Then the cURL will look like this.
curl -v -su '' -H 'Accept-Version: v10' -H "Content-Type: application/json" -X POST -d '{"order_id":"subtest","amount":"100"}' https://api.quickpay.net/subscriptions/1234/recurring