If the first approver has submitted an overtime compensation request, but the applicant does not have any overtime available at the time of approval, then simply nothing happens when you click on the green checkmark.

The application stops and nothing happens.

An error message would be good here — e.g. “currently not enough overtime available”.

Case from practice:

The applicant had forgotten to enter his hours for the last 2 days (since there was a 3-day deadline) and therefore did not have enough hours available today for the overtime compensation application, which had already been submitted for 2 weeks.

The first approver now clicks on the green checkmark and wonders why the application doesn't disappear or there is no error message.