In order to successfully create a customer, the 3 steps listed below are required:

Create Customer
Create Payment Method
Link Customer to a Payment Method

Refer to each individual sections in the API reference guide to see what APIs have been listed in order to achieve this.

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Helpful Tips:

When creating a customer, the email address field is compulsory. It needs to be unique for every customer. The system will not allow for duplicate email addresses.

Every customer must have at least 1 payment method linked. If they have multiple payment methods, all the payment methods stored against the customer cannot be deleted. The primary payment method will always remain.

Asynchronous calls have timed interval settings. It is required to wait 1-2 seconds before firing the post API in order to add a payment method to a customer.