Your solution has more than one problem, probably caused by somewhat confusing description. First of all, you do not apply the odd/even multipliers correctly, your call to mapi is not correct. Then you do not reduce the obtained numbers to single-digit ones.

You need to fix your solution. In case of problems, you can ask for help in #help-solve channel of CW Discord.

Language: F#
It fails test 1-4 and 6 but all other passes, manually testing it works fine on my end.

Approved

Lua translation and Prolog translation

Fixed.

Self-approved :)

Added random tests to CoffeeScript

Double every other digit, scanning from right to left, starting from the second digit (from the right).

Whilst your code is doubling every digit.

Your solution is wrong and fails with inputs like 8675309 it returns true instead of false.

8675309 ==> [8, 6*, 7, 5*, 3, 0*, 9] ==> [8, 12, 7, 10, 3, 0, 9] ==> [8, 3, 7, 1, 3, 0, 9]
[8, 3, 7, 1, 3, 0, 9] ==> [8, 3, 7, 1, 3, 0, 9] = 31
31 (modulus) 10 ==> 1 , which is not equal to 0, so this is not a valid credit card number

Not a kata issue.

If a resulting number is greater than 9, replace it with the sum of its own digits (which is the same as subtracting 9 from it)

You're not doing that right.

Everything is working on my end, and I am passing the test. But when I attempt, it is saying expected true to equal false and vice versa if I change.

Scala translation

Good problem!

Nice, thanks for that @hobovsky. Indeed, it's passing now.

I changed the reference solution which seemed to be buggy, and your solution passes now. Please verify and mark the issue as resolved if the problem does not occur anymore.

Should be fixed.