Javascript – Uncaught TypeError: Cannot set properties of undefined (setting 'weight')

i´m trying to handle the state of my input fields in react via my handleChange method. It works fine for my titles (exercise name) but not for the input fields below my titles (reps and weight)

export const Workout = () => {
  const initalExercises = [
    {
      title: "Bench Press",
      sets: [
        {
          reps: 1,
          weight: 80,
        },
        {
          reps: 2,
          weight: 80,
        },
      ],
    },
    {
      title: "Squat",
      sets: [
        {
          reps: 2,
          weight: 90,
        },
        {
          reps: 4,
          weight: 90,
        },
      ],
    },
  ];
  const [exercises, setExercises] = useState(initalExercises);



  // //handles input change

  const handleChangeTitle = (e, exercisesIndex) => {
    const { value } = e.target;
    const onChangeVal = [...exercises];
    onChangeVal[exercisesIndex].title = value;
    console.log(value);

    setExercises(onChangeVal);
  };

  const handleChange = (e, exercisesIndex, setIndex) => {
    const { name, value } = e.target;
    const onChangeVal = [...exercises];
    onChangeVal[exercisesIndex].sets[setIndex][name] = value;
    setExercises(onChangeVal);
    console.log(onChangeVal);
  };

here is my jsx

  return (
    <div className="exercisesWrapper">
      <div className="exercisesContainer">
        {/* <button onClick={addExrc}>Add Exercise</button> */}
        {
          <button className="addExrc" onClick={addExercise}>
            Add Exercise
          </button>
        }

        {exercises.map((exercise, exercisesIndex) => (
          <div key={exercisesIndex}>
            <div>
              <button
                className="deleteExrc"
                onClick={() => handleExerciseDelete(exercisesIndex)}
              >
                -
              </button>
              <input
                className="inputField"
                id="titleInput"
                name="title"
                type="text"
                placeholder="Exercise"
                value={exercise.title}
                onChange={(e) => handleChangeTitle(e, exercisesIndex)}
              />
              <button
                className="addSet"
                onClick={() => addCurrentSet(exercisesIndex)}
              >
                + Add set
              </button>

              {exercise.sets.map((set, setIndex) => (
                <div
                  key={`${exercise.title}-${setIndex}`}
                  className="currentSetInput"
                >
                  <input
                    className="inputField"
                    name="weight"
                    type="text"
                    value={set.weight}
                    onChange={(e) => handleChange(e, setIndex)}
                  />
                  <input
                    className="inputField"
                    name="reps"
                    type="text"
                    value={set.reps}
                    onChange={(e) => handleChange(e, setIndex)}
                  />

                  <button
                    className="deleteSet"
                    onClick={() => handleDelete(exercisesIndex, setIndex)}
                  >
                    -
                  </button>
                </div>
              ))}
            </div>
          </div>
        ))}
      </div>
    </div>
  );

Every other function is working fine its just the handling of my weight and reps input thats not working