twoSum Algorithm : How to improve this?

Question

I felt like doing an algorithm and found this problem on leetcode

Given an array of integers, find two numbers such that they add up to a specific target num

Answer 1

Just curious, but what's wrong with this O(n) solution?

public int[] twoSum(int[] nums, int target) {
    for (int i = 0; i < nums.length - 1; i++){
        if (nums[i] + nums[i+1] == target)
            return new int[] {i, i+1};
    }
    return null;
}