SK Key Generator tool allows you to generate free valid SK live keys for stripe based cc checker. It generates random SK keys, so it doesn't promise 100% accuracy.
Try Demo: https://checkz.co/sk-key-generator
If you encounter a bug, I would very much appreciate that you can contact me (https://checkz.co/) that explains the nature of your bug. Please include details like which browser version you're using and the steps to reproduce the bug. Other comments are welcome.