I found workaround:
add_action( 'admin_footer', function() {
?>
<script type="text/javascript">
var tmp_acf_serialize_form = acf.serialize_form;
acf.serialize_form = function( $el, prefix ) {
var data = tmp_acf_serialize_form( $el, prefix );
data['post_id'] = <?php echo get_the_id(); ?>;
return data;
}
</script>
<?php
} );
and now in add_filter( 'acf/validate_value/...
you can use $_REQUEST['post_id'];
There’s needs to be checked if acf exists in js…