Yes, it is possible to build a credit card form with Stripe that includes a variable fee, such as a 4% fee added to the total amount. Bit Form offers a Dynamic Option, which allows you to customize the final payment amount. You can use this feature to add a variable fee (like 4%) to the total amount field before charging the user through Stripe.

Here is a demo video showcasing how this can be done: https://jam.dev/c/ef42dfcf-53b5-443d-97c4-b90bf39ecf92