Hi @F_M!
IF() formulas work as follows:
IF({condition is true/has a value},
{do this},
{otherwise do that}
)
In your case you need to create your new field of choice and then add an IF() statement to your original formula. This should do it.
IF({name of new field of choice},
{name of new field of choice},
{Payment from Customer}*({Auto Calculated Percentage}/100))-{Admin Fee}-{Insurance Fee}-{Amount Paid to Employee}
)
(You have a random ‘(’ at the beginning of your formula. Check to see if this is a mistake just in your question post or if not all of your original formula was copied. Make sure that you use the whole of the original formula in your IF()-statement for it to work as desired.)