Please look into below issue in one testcase

#1

so i am solving this problem:https://leetcode.com/problems/split-array-largest-sum/description/

now below is my code:
class Solution {

private:
int func(vector& nums, int sum)
{
int cnt=1;
int cummSum=0;
for(int i=0;i<nums.size();i++)
{
if((cummSum+nums[i])<=sum)
{
cummSum=cummSum+nums[i];
}

     else if((cummSum+nums[i])>sum)
     {
         cummSum=nums[i];
         cnt++;
     }
 }
 cout<<cnt;

return cnt;}

public:
int splitArray(vector& nums, int k) {

        int cnt=0;
    if(nums.size()<k)
    {
        return -1;
    }
    
    int minCap = *max_element(nums.begin(), nums.end());
    cout<<"minCap "<<minCap;
int maxCap = accumulate(nums.begin(), nums.end(), 0);

    for(int sum=minCap;sum<=maxCap;sum++)
    {
         cnt=func(nums,sum);
        if(cnt==k)
        {
            return sum;
        }
    }






return 1;}

};

why is the below testcase failing:[2,3,1,1,1,1,1] k=5