Have you tried to print get_field('field_5b303fe622a15') ? Maybe it’s a subfield ?
I’ve tested this code on a WP loop and it worked :
$count = (int) get_field('count');
if ( $count >= 0) {
$count++;
update_field('count', $count);
}
By the way, get_field and update_field can be used with the field’s name instead of the field’s key.
