Code Code Credit Card Validator : Test Case 4 invalid result

Question

I am doing the Code Coach challenges.

I am try to solve the Credit Card Validator.

Test Case 4 keeps failing.
I have tested all results in between, with the sample input. That comes out correct.

Can some one give me a hint, what is tested in Test Case 4.
Or why my code fails in test case 4.
https://code.sololearn.com/cuTQtxAdoj8R

Answer 1

The "Subtract 9 from all numbers higher than 9" part needs a small fix. You'll find it out :)

Answer 2

Thank you. That was exactly what I needed to know. Stupid bug. Problem solved.