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.
Once you've logged in to your account, use the burger menu on the left side to see your available textures and render packs. Use the green plus sign near the item to purchase it.