You have the possibility of buying additional credits when you are on a paying subscription.
You can check your credit balance from the top banner.
If you have no credits left and you need more, click on the credit balance and press "Get more credits". You will be redirected to a page where you can top up your credits.
Just choose the amount of credits you want to buy and you will be forwarded to a payment link. You will get access to your credits immediately after purchasing.