The red arrow points to the line that gives the total of all your deposits. This line has 5 places to the left of the decimal point.
The blue arrow points to the line in which you write how much cash back you want. This amount should be zero or positive. This line also has 5 places to the left of the decimal point.
The green arrow points to the line giving the total amount to deposit. It equals the amount on the red-arrow line minus the amount on the blue-arrow line. This line has 6 places to the left of the decimal point.
How can you possibly subtract a 5-digit number from a 5-digit number and end up with a result that requires 6 digits?