Can’t set Post ID properly

I’m trying to generate posts based on a JSON document. I’m stuck at the trying to assign the ID from the json document to the post’s wordpress ID. I read on here that the way of going about this is though setting an ‘import_id’ on wp_insert_post

$  json = json_decode("{         \"tt1412213\":{            \"title\":\"Movie\",            \"rating\":\"excellent\"         }     }", true);  foreach($  json as $  item) {      $  itemID = array_keys($  filmJson, $  item);     if (get_post_status( $  itemID ) == false ) {         if($  item["title"] and $  item["rating"]){             global $  user_ID;             wp_insert_post(array(                 'post_title' => $  item["title"],                 'post_content' => $  item["rating"],                 'post_status' => 'publish',                 'post_date' => date('Y-m-d H:i:s'),                 'post_author' => $  user_ID,                 'post_type' => 'post',                 'post_category' => array(0),                 'import_id' => $  itemID             ));         }     } } 

I would like my post to have the ID tt1412213 but it defaults to a number instead. Anything I’m missing?