$media_id = "UNK.0xF3100226.bb43e7f35adf889462505e3801b8ce44";

$url = "https://api.weixin.qq.com/cgi-bin/media/get?access_token={$accessToken}&media_id={$media_id}";

请求$url后得到 {"errcode":40007,"errmsg":"invalid media_id hint: [n_WOka0123p448] rid: 6757b0bb-0ebfcfbb-1ad3124c"}