Slice and Splice - Console returns Correct result but on Submission, I'm Getting Error

Sorry to disturb everyone but, I just finished writing a code for one of the “Basic Javascript Algorithm Scripting” challenge. The console returns the required answer but I can’t seem to go to next challenge with this code I’ve written.
I also want to say that "This section of Javascript - “Basic Javascript Algorithm Scripting” is tough. lol. I’ve been wanting to rush it like I was doing others, but so far I’ve checked the hint page twice for two challenges and the ones I solved took me so much time to code.

function frankenSplice(arr1, arr2, n) {
  // It's alive. It's alive!
  let arr3 = arr2.slice();
  arr3.splice(n, 0, arr1.slice());
  return arr3;

console.log(frankenSplice([1, 2, 3], [4, 5, 6], 1));
console.log(frankenSplice([1, 2], ["a", "b"], 1)); 
console.log(frankenSplice(["claw", "tentacle"], ['head', 'shoulders', 'knees', 'toes'], 2));

Here’s an image of my solution

Your browser information:

Link to the challenge:

Open up the browser console and look at what is being logged, can you see the problem?

Oh wow. I got a 2 dimensional array.
I should have checked my browser console before posted this.
Thanks alot for your advice @lasjorg