If you have been charged for a small amount after signing up for a free plan with potential overage costs, aka "Freemium", you are seeing a pre-authorization charge.
What is a pre-authorization?
A pre-authorization is essentially a temporary hold for a small amount of money placed by a merchant on a customer’s card, in this case to verify if there are funds available on that card, for a period of 1 week. After that time the hold is released, these funds are never kept by RapidAPI.