IF(ISERROR combined with (Mod(Month

I have a formula that matches a start month to a horizontal calendar range. This is the formula: =IF($I$17>=$F18,IF(MOD(MONTH($I$17)-MONTH($F18),$D18)=0,$E18,0),0)

When the match is found it takes a defined value and enters the value in that month. It also then extrapolate the same value every n number of months. This n number of months is defined.This is what the result looks like for the above formulaPay $375 every 2nd month starting in Nov 18

The problem I can't fix is when the "Pay every # months" is blank the result is #DIV/0!. The month frequency is blank I know that it should be fixed by using the IFERROR or IF(ISERROR function but I just can't seem to get it right. Any help will be welcomed please