Yes, as the title suggests

Given an array arr, find element pairs whose sum equal the second argument arg and return the sum of their indices.

What I have done so far

function pairwise(arr, arg) {
  if (arr.length === 0) return 0
  let res = [];
  let indexes = [];
  let indexArr = []
  for (let i = 0; i < arr.length - 1; i++) {
    for (let j = i + 1; j < arr.length; j++) {
      if (arg === arr[i] + arr[j] && !indexes.includes(i) && !indexes.includes(j)) {
        res.push([arr[i], arr[j]]);
        indexes.push(i);
        indexes.push(j);
      }
    }
  }
  console.log(res)
 
  for (let i = 0; i < res.length; i++) {
    for (let j = 0; j < res[i].length; j++) {
      indexArr.push(arr.indexOf(res[i][j]))
    }

  }

  return indexArr.reduce((curr, prev) => curr + prev)
}

pairwise([1, 1, 1], 2);

I am doing this in Freecodecamp. It passes some test but fails the following tests:

pairwise([1, 1, 1], 2) should return 1. (above code returns 0) pairwise([0, 0, 0, 0, 1, 1], 1) should return 10. (above code returns 8)

I think I am doing wrong in the indexOf part. How to solve this?