Google Cloud Functions is another online service where you can run arbitrary Python code "in the cloud" (on Google's servers). They have a free tier. And if you want to use it... you have to give them your credit card information. That's just how services like these work.

Reflex has nothing like that: you can't run your Python code on their servers, yet --- and once you can, you can be sure they're not going to let you try it for free without asking for your credit card.