Hi guys here is the issue.

Under column A, which is titled serial number, I have listed the formula
=IF(ISNUMBER(B28)=TRUE,A27+1,""). What this does is that it detects if there
is a date in column B and then inputs a serial number that is one more than
the previous one. If not the cell in column A is just left blank if no date
is detected.

Under column D, entitled Receipt number, I have inputed the formula
=IF(MOD(A27,8)=0,"","NA"). What this does is it detects the serial number in
column A and checks if it is a muliple of 8. If it is the cell in column D is
left blank. If not "NA" is displayed. However if there is no serial number at
all, I get a #VALUE! symbol.

To get rid of the symbol, I tried a new formula in column D,
=IF(ISNUMBER(A28),IF(MOD(A28,8)=0,"","NA"),"")
What I am trying to achieve is that if no number is detected in column A,
then column D should remain blank. If there is a number detected, then
=IF(MOD(A28,8)=0,"","NA") should be applied. However, this does not seem to
work. What am I doing wrong?