This error can be due to two situation: -

1) The date that you wish to apply is not a working day

2) You tried to apply only half-day (AM or PM), but you got insufficient half-day.

To check (1)
1) Login to WhyzeHR
2) Go to "Basic HR" module
3) Go to "Setup"
4) Click "Calendar"
5) Click "Work Time Profile"
6) Locate the Work Time Profile of your employee and click into it
(If you unsure, go to Basic HR ---> employee ---> Click into employee profile ---> Under "employment" tab, you can know from there)
7) Scroll to bottom, click "Calendar" tab ---> click "2025"
8) You will see list of months, click "+" to expand the month you wish to check
9) Take a look is the "Leave Pattern" is FULL/HALF or OFF? If this date is a working day, it is supposed to be FULL/HALF. Click into the date to change it will do.

To check (2)
1) Login to WhyzeHR
2) Go to "Leave" module
3) Go to "Setup" ---> Go to "Leave Type"
4) Locate and click into the Leave Type that you intend to apply
5) Scroll to bottom and look for "Mapping" tab, verify which mapping belongs to the employee and click into it
(If you unsure, go to Basic HR ---> employee ---> Click into employee profile ---> Under "career" tab, you can know from there)
6) You should able to see there is "Allocation" at the bottom, look for a header call "Max Half Day", is it showing 0? You can take a screenshot and share to me if you unsure.