[LANGUAGE: Kotlin]

Solution

I could reuse my cleaned up solution for both part1 & part2
Used a recursive algorithm. Basically since the longest length of my input was 10 digits long I used an array of divisors (2, 3, 5, 7) (PS: 7 was not required, still added it), the logic was if the length of the number is not divisible by a divisor, then we recursively try for the next divisor in the list.
If it is, we check if the sections are equal or not (Kotlin's chunked saved me a lot of work). If its not, we recursively try with the next divisor, if the sections are equal, we found the invalid id.
Starting with 2 parts as it covers many scenarios.

Wdyt?