php 缓存token在session的问题？

不知道为什么第一次请求的token为空（过期之后请求的第一次 ） 第二次就可以 请求大神帮忙看看我要把token保存起来，要不然请求的接口次数不够用

<?php
header("Content-type:text/html;charset=utf-8");
session_start();
//接收post过来的 json数据
$data = json_decode(file_get_contents('php://input'), true);
$userPhone=$data['userPhone'];
$message=$data['message'];
$serNumber=$data['serNumber'];//编号
$username=$data['username'];//发起人
$processCategory=$data['processCategory'];//流程类别
$remark=$data['remark'];//备注
$sendTimestr=$data['sendTimestr'];//发起时间

//var_dump($data);die;
//print_r($sendTimestr);die;

$conn = mysqli_connect("192.168.0.232", "root", "@jjgw6201", "user_wechat");
$wxresult=mysqli_query($conn,"select * from user_wechat where PHONE_NUM = '$userPhone'");
$result = mysqli_fetch_array($wxresult, MYSQLI_ASSOC);

if(!empty($_SESSION['access_token']) && $_SESSION['expire_time'] > time() ) {
    //var_dump($_SESSION['access_token']."|".$_SESSION['expire_time']."|".time());die();
    $url = "https://api.weixin.qq.com/cgi-bin/message/template/send?access_token=" . $_SESSION['access_token'];
    // var_dump(date("Y-m-d H:i:s", $_SESSION["expire_time"]));die();
    $template = [
    'touser' => $result['OPEN_ID'],  //openid
    'template_id' => "Jg8Ow95NYuepZ08J91bDbNzyZM5e9SZSC4eJ4PCe3HA", //前面新增的模板id
    'data' => array(
    'first'    => ['value' => urlencode("$message")],
    'keyword1' => array('value' => urlencode("$serNumber")),//编号
    'keyword2' => array('value' => urlencode("$username")),//发起人
    'keyword3' => array('value' => "$sendTimestr"),  //发起时间
    'keyword4' => array('value' => urlencode("$processCategory")),  //流程类别
    'remark'   => array('value' => urlencode("$remark")) //备注
    )
                ];
    $json_template = json_encode($template);
    $json_template1 = urldecode($json_template);
    $curl = curl_init();
    curl_setopt($curl, CURLOPT_URL, $url);
    curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, FALSE);
    curl_setopt($curl, CURLOPT_SSL_VERIFYHOST, FALSE);
    curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($curl,CURLOPT_POSTFIELDS,$json_template1);
    $output = curl_exec($curl);
    //curl_close($curl);
    $output = json_decode($output,true);
    var_dump($output);
}
else
{
    //echo "2";die;
    // 过期了
    //print_r($result['OPEN_ID']);die();
    $app_id = 'xxx';
    $app_secret = 'xxx';
    //请求微信接口获取access_token
    $token_url = "https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid={$app_id}&secret={$app_secret}";
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $token_url);
    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE);
    curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, FALSE);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    // curl_setopt($ch, CURLOPT_HTTPHEADER,$headerArray);
    $output = curl_exec($ch);
    //curl_close($ch);
    $output = json_decode($output,true);
    //var_dump($output);
    $access_token = $output["access_token"];
    //存储session
    $_SESSION['access_token']=$access_token;
    $_SESSION['expire_time']=time()+120; //秒
    return $_SESSION['access_token'];
}