Hi,
legal requirement is to deduct until zero, even if deduction exceeds per diem. Deduction amount can never be negative if per diem is available for day of travel.
But pls do not forget settings for taxable amount in case of days without per diem. In that case, there is deduction of -1,63 for breakfast and -3,00 for lunch/ dinner, which must be either deducted from trip total or forwarded to payroll for taxation.
rgds, Michael