how to get the values of other fields in acf validate values
add_filter('acf/validate_value/key=field_56e069e986d6f', 'my_validate_function', 10, 4);
function my_validate_function($valid, $value, $field, $input) {
$other_field_key = 'field_56e06fe24d3e7';
$other_value = $_POST['acf'][$other_field_key];
// now you can do validation based on the other value
return $valid
}