While a subscription is an auto-renewable payment (that will be charged off your card every month/year), renders and textures are one-time purchases.
With a one-time payment, you receive a limited amount of items. Once you’ve used up all items, you will need to make another purchase.
You can do that from the Profile section by clicking on the Plus sign near the available amount of textures or renders. Once the payment is charged and confirmed, you will receive a top-up of purchased items.