[Biginner]Zbrush displacement export problem

vakdlfjas

hi merry christmas

i've managed to sculpt my first face and i wanted to export displacement map for arnord

and i keep getting this result

 I think i've tried everything like changing subdivision catclark displacement attributes like scalar zero value colorspace 
and i've realized that the map itself might be the problem because



this is what i got when i opened it with photoshop 

setting i used

 

UV i just focused on the face that i was going to see for quick test could it be the problem?

So 
first,  i sculpted face on zbrush
second, after that i made low poly version and did quick UV for test 
third, i used project all and clean up some artifacts and detail again
last, export displacement map ( lowpoly 16000 / highpoly 16m)

did i do something wrong? 

Thanks