I need help with hiding a negativ value!!!!

In cell A6 I have:

=A6-A4

But I just want to hide the value in A6 when it turns negative and not
change to whole value to 0

I have been reading other posts but nothing works.

=IF(A6 <0,0,A6)

excel just says that the formula contains an error! I don't put the
formula "=IF(A6 <0,0,A6)" in cell A6


thx for your help!