Your customers can be added automatically into eCurring in two different ways:
1. Through a subscription page/iFrame
When customers sign up through a signup form, they automatically get added into eCurring. Because the signup form has a product connected to it, a subscription for that product gets automatically created on this customer. Once the customer has issued their mandate the subscription will become active and transactions will be created within 10 minutes.
2. Through the API
You can also choose to add your customers through the eCurring API. Documentation for that can be found here: