Don't know what I did wrong with the logical operator "OR"

I don't find my mistake in the following formula

=if(AB207<=DATE(2019,8,1),(Z207*0.075),(Z207*0.15);OR if Date =(#N/A)(Z207*0.15))

I want the Formula to multiply the cell Z207 with 0.15 if the "value" is #N/A

Hope someone can help me