not sure if I am looking at this wrong, but from what I see in the code, the dump of $currency shouldn’t be an array
this bit here
<?php
if(have_rows('currencies', 'option')): while(have_rows('currencies', 'option')): the_row();
$currency = get_sub_field('currency');
endwhile; else : endif;
?>
This would overwrite the value of $currency with each iteration, try changing it to
<?php
$currency = array();
if(have_rows('currencies', 'option')): while(have_rows('currencies', 'option')): the_row();
$currency[] = get_sub_field('currency');
endwhile; else : endif;
?>
and because currency is defined, you can eliminate the if($currency) and just use the in_array()
