首先讲两个注意事项

1、小程序和微信公众号的用户openid是不同的。

2、小程序需要用户手动授权订阅消息通知（一次性订阅是订阅一次发一次，长期订阅可以多发）。

关于小程序和公众号AppID和AppSecret的获取可以自行百度一下，挺简单的。

小程序订阅消息

1.1 在后台选中自己需要的模板和相应的字段，注意不同的字段字符长度和格式的问题。

参考文档：subscribeMessage.send | 微信开放文档

【订阅消息参数值内容限制说明】

1.2 小程序授权按钮

<button class="btn" bindtap="onSubscribe" hover-class="btn-hover">
  订阅挂号成功提醒
</button>

//开启消息通知
onSubscribe: function(e) {
    // 消息推送
    wx.requestSubscribeMessage({
      tmplIds: ['daPvT7nLnOY***************F_A9VCBI'],  //你的模板id
      success(res) {        
        console.log('授权成功', res)
      },
      fail(res) {
        console.log('授权失败', res)
      }
    })
},

1.3 我这里用的HTTPS发送，代码是php

<?php
    /*
     * 微信小程序消息订阅
    */ 
    public function actionSubmessage($openid = null){
        //配置appid
        $appid = "";
        //配置appscret
        $secret = "";
        $url="https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid=".$appid."&secret=".$secret;
        //获取access_token
        $access_token = $this->geturl($url)["access_token"];

        $urlz="https://api.weixin.qq.com/cgi-bin/message/subscribe/send?access_token=".$access_token;
        //模板id
        $template_id = "daPvT7nLnO*********************A9VCBI";
        $data = [] ;
        //接收者（用户）的 openid
        $data['touser'] = $openid;

        //所需下发的订阅模板id
        $data['template_id'] = $template_id ;

        //点击模板卡片后的跳转页面，仅限本小程序内的页面。支持带参数,（示例index?foo=bar）。该字段不填则模板无跳转。
        $data['page'] = "pages/index/index" ;

        //模板内容 phrase  date thing 这些类型有字符长短要求，注意看文档
        $data['data'] = [
            "phrase2" => [
                'value' => '测试'
            ],
            "phrase6" => [
                'value' => '就诊李主任'
            ],
            "date14" => [
                'value' => '2022年06月11日'
            ],
            "date8" => [
                'value'=>'8:30 ~ 17:00'
            ],
            'thing18'=>[
                'value'=> '呼吸内科'
            ]
        ];
        //跳转小程序类型：developer为开发版；trial为体验版；formal为正式版；默认为正式版
        $data['miniprogram_state'] = 'developer';
        var_dump($this->posturl($urlz,$data));
    }

    /*
    * curl get请求封装,返回json数据格式数据
    */
    public function geturl($url){
        $headerArray =array("Content-type:application/json;","Accept:application/json");
        $ch = curl_init();
        curl_setopt($ch, CURLOPT_URL, $url);
        curl_setopt($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);
        return $output;
    }

    /*
     * curl post请求封装,返回json数据格式数据
    */
    public function posturl($url,$data){
        $data  = json_encode($data);
        $headerArray =array("Content-type:application/json;charset='utf-8'","Accept:application/json");
        $curl = curl_init();
        curl_setopt($curl, CURLOPT_URL, $url);
        curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, FALSE);
        curl_setopt($curl, CURLOPT_SSL_VERIFYHOST,FALSE);
        curl_setopt($curl, CURLOPT_POST, 1);
        curl_setopt($curl, CURLOPT_POSTFIELDS, $data);
        curl_setopt($curl,CURLOPT_HTTPHEADER,$headerArray);
        curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1);
        $output = curl_exec($curl);
        curl_close($curl);
        return json_decode($output,true);
    }
?>

公众号模板消息推送 

2.1 微信公众号开启模板消息推送

 2.2 这个前端没啥特别的，直接上后端代码，用的tp6框架，可以根据实际情况自己改

类文件 WxMessage.php

<?php
//WxMessage.php
namespace Think;
class WxMessage
{
    //服务号
    var $appid = ''; 
    var $appsecret = '';

    //构造函数，获取Access_Token
    public function __construct($appid = NULL, $appsecret = NULL)
	{
		if($appid && $appsecret){
			$this->appid = $appid;
			$this->appsecret = $appsecret;
		}

        //$this->lasttime = 1654756504;
        //$this->access_token = "57_cu07w68F9BPur3VvmkFPS6i_OLkN5dGJeCeJn8u8PKNRgxOmQ4PtCVesDNFwIj-6ExGmHhM2vzoparead5OnW7FZmuYWEyr2JwszreshbNdDQ8mtDaGncwnbgVVXjf8UKvaagCfqOct5hS97ZQHhAFALCT";

        //if(time() > ($this->lasttime + 7200)){
        	$url = "https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid=".$this->appid."&secret=".$this->appsecret;
			$res = $this->http_request($url);
			$result = json_decode($res, true);
            //echo $result["access_token"];
			$this->access_token = $result["access_token"];
			$this->lasttime = time();
	    //}
	}

	public function send_template_message($data)
	{
		$url = "https://api.weixin.qq.com/cgi-bin/message/template/send?access_token=".$this->access_token;
		$res = $this->http_request($url, $data);
		return json_decode($res, true);
	}

	//https请求(支持GET和POST)
	protected function http_request($url, $data = null)
	{
		$curl = curl_init();
		curl_setopt($curl, CURLOPT_URL, $url);
		curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, FALSE);
		curl_setopt($curl, CURLOPT_SSL_VERIFYHOST, FALSE);
		if (!empty($data)){
			curl_setopt($curl, CURLOPT_POST, 1);
			curl_setopt($curl, CURLOPT_POSTFIELDS, $data);
		}
		curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1);
		$output = curl_exec($curl);
		curl_close($curl);
		return $output;

	}
}
?>

<?php
namespace app\admin\controller;
use think\Controller;
use think\Validate;
use think\facade\Request;
use think\facade\Db;
use think\facade\Session;
use think\facade\View;
use think\WxMessage;  //引入类

class Weixinqf extends Base
{     
    //发送提醒    
    public function sendMessage(){       
    	//构造消息模板
        $openid = "";  //自己去获取
        $zname = "程序测试";
        $zsource = "公众号—就诊(李主任)";
        $zdate = "2022-06-08(上午)";
        $template = $this->orderSuccess($openid,'',$zname,$zsource,$zdate);  
        
        //实例化消息类
        $message = new WxMessage();
        //发送消息
        $message->send_template_message(urldecode(json_encode($template)));
    }

    //成功通知模板
	/*
	 * openid:微信唯一标识
	 * zname:姓名
	 * zsource:来源
	 * zdate:时间
	 */
	public function orderSuccess($openid=null,$url=null,$zname=null,$zsource=null,$zdate=null){
	    $template = array(
	        "touser" => "{$openid}",
	        "template_id" => "7zQSy****************KOlsc",
	        //'url' => "{$url}",  //也可以配置这个，就可以进入自己配置的网址
	        "miniprogram" => array(  //我这里引入的小程序
                "appid" => "*******", "pagepath"=>"pages/index/index"
            ),   
	        'data' => array(
	        	'first'   => array('value' =>urlencode('挂号成功'),'color' => "#FF0000"),
	            'keyword1' => array('value'=>urlencode($zname)),
	            'keyword2' => array('value'=>urlencode($zsource)),
	            'keyword3' => array('value'=>urlencode($zdate)),
	            'keyword4' => array('value'=>urlencode('8:30 - 17:00')),
	            'keyword5' => array('value'=>urlencode('呼吸内科')),
	            'remark'   => array('value'=>urlencode('凭预约短信和就诊人身份证在门诊一楼导医台取号就诊，一对一问诊，医务人员全程陪同。详情请咨询：028-******！'),'color' => "#FF0000"),
	        ),
	    );
	    return $template;
	}
}

?>