hamiknk: that's for Go, while Khath1d3 used C#.

you can debug test cases with next lines
func QueueTime(customers []int, n int) int {

fmt.Fprintln(os.Stdout, "Input:", customers)
fmt.Fprintln(os.Stdout, "Tills", n)

...

You used Issue label, that's reserved for problems with the kata itself. Use Questionif you want to use a label for cases like this. And I already told you how to print the input to help you debug your code. You can also provide your code following this guideline: https://docs.codewars.com/training/troubleshooting/#post-discourse

A problem with your code is not a kata issue. Please read this about how to print the input and debug your code: https://docs.codewars.com/training/troubleshooting/#print-input

which is the number of times you must multiply the digits in num until you reach a single digit.

That's what it says in the description, it doesn't say "return the single digit".