Hey there, @Riazell
Bo here from Shopify Support!
This could be due to a few different things. Could you open the product in your admin and take a look at your inventory settings? While the item is digital, it can still be limited due to inventory as some sellers will only want to sell a certain amount of a digital product. Your inventory settings should look like this:
If all looks right and you are still experiencing this issue, please send me a link to the product in question. I would highly recommend checking out our post on what information to give when looking for support in the community so you are better equipped to ask for support.
All the Best,