When a product is fully configured, the customers can use Project X API Checkout Links to subscribe.
If the product is free of charge or is pay-per-use, the subscription gets activated instantly and an access token is issued. It can be found on the subscription page in the API consumer portal.
If the product is not free, a newly created subscription becomes "Incomplete" until the first payment is made.
At this point, there is no access token issued and the customer has no access to the APIs included in it.
In order to activate it, the customer has to pay the first invoice. Once it's paid and the payment is processed, the subscription is moved into the "Active" status.
If the first invoice is not paid within 24 hours after subscription creation, the subscription becomes "Incomplete expired", the invoice is voided and can't be paid anymore. The customer has to create a new subscription.
Whenever an invoice is not paid after its due date, the subscription is moved into Past due status. At this point, the customer can still access your product. If the payment is not received and the payment due date has passed, the subscription becomes Unpaid.
At this point, customer's access is revoked and the most recent invoice has to be paid in order to restore access.