Shortcode not passing variable to included file

Ok, so somehow I got it working by changing it to this:
It looks like it didn’t like ‘the_clientId’. Maybe it just doesn’t like capital letters????

[insert-form form_location="form.php" identification_number="12345"]


function insert_the_form($atts){
  $form_base = plugin_dir_path(__DIR__);

  // Shortcode attributes & options
  $atts = shortcode_atts(
  array(
    'form_location' => 'NULL',
    'identification_number' => 'NULL' //Variable for client ID
    ), $atts, 'insert_the_form'
  );

if ( isset($atts['form_location']) ){
  $form_location = $atts['form_location'];
}
if ( isset($atts['identification_number']) ){
  $form_idnumber = $atts['identification_number'];
}   

$clientId = $form_idnumber;

ob_start();
include($form_base . 'forms/' . $form_location);
$out = ob_get_clean();

return $out;
}

add_shortcode( 'insert-form', 'insert_the_form' );