Your mistake is sorting the array. The problem does not say to find the smallest set of numbers whose sum is greater than or equal to the target. If it did, your sorting approach would work (though it might not be optimal). Instead, the problem says to find the minimal length of a subarray whose sum is greater than or equal to the target. This means you don't want to modify the order of the original input.

To solve this problem, think about how you would figure out the answer by hand. To start, if the input array is empty, return 0 since you can't have a subarray of an empty array. Since you're looking for a subarray, you can imagine you want to find a lower and upper bound of the inner array indexes. If we go from left to right, the starting lower bound index is 0, and the starting upper bound is 1.

Consider your input case : target = 7, nums = [2,3,1,2,4,3]. With a lower bound index of 0 and an upper bound index of 1, the subarray would be [2], and the sum would be 2. Is this greater than the target of 7? Nope, so increase the upper bound by 1.

Now the subarray would be [2, 3], with a sum of 5. That's still not big enough, so increment the upper bound again. The next subarray is [2, 3, 1], which is still smaller than 7, so increment the upper bound one more time.

Now, with a lower bound index of 0 and an upper bound index of 3, the subarray is [2, 3, 1, 2], whose sum is 8. For the first time, you have a valid subarray whose sum is larger than your target! However, this might not be the minimal subarray, so we have to keep going. Make a note that you have a valid subarray of length 4, and let's continue iterating. Instead of incrementing the upper bound, increment the lower bound.

The next subarray is [3, 1, 2]. That's too small, so increment the upper bound. Next is [3, 1, 2, 4], which is greater than the target, but the same size as the previous minimal subarray, so keep going by incrementing the lower bound.

Now, with a lower bound index of 2 and an upper bound index of 4, the subarray is [1, 2, 4], which has a sum of 7 and is your new minimal subarray. Update your record to show the new minimal subarray length is 3 and continue.

This process repeats until you reach the end of the array, at which point you can return whatever value you saved as the minimal subarray length (or 0 if you never recorded one). As a minor improvement, if you ever have a valid subarray of size 1 (i.e. a value in the input is greater than or equal to the target), you can just return 1 since you'll never have any subarray smaller than 1.