“Do I have to add a credit card to test it?”

This would be a question to ask RapidAPI support about, but, I believe you do require an account and credit card on file to test services, but you wouldn’t be charged if you use the ‘test’ feature or the 100 free image per day option. Of note, we have two endpoints, a Nudity API service and a new NSFW API that provides additional labels not included in the Nudity API.