hello
please help me with iserror or isna with conditinal formating

i've got a whole column with vlookup,
a
1234
114315
123512
#N/A
1231

i wanted to fill box for those #N/A
i clicked the column A and tried;

=ISNA(A1), =ISNA($A1)
=ISERROR(A1), =ISERROR($A1)
=ISNUMBER(A1), =ISNUMBER($A1)
NOTHING WORKS!!!

can someone tell me why this isn't working?

thank you!!