我正在处理nginx和node express服务器，该应用程序用于通过端口80的反向代理工作正常，但当我在nginx上安装SSL与certbot时开始出现问题，我一直在尝试https节点模块，但当我从我的Angular 前端向我的节点后端发出请求时，我仍然会收到混合内容错误。我认为这是一个糟糕的流量配置在nginx，也许我需要设置流量从nginx到节点服务器（端口3000）与http，但我不知道如何实现这一点。先谢谢你了。
请求时出现控制台错误：
polyfills-es2015。aa82454585d558e1759e。js：1混合内容：页面在'https：//www.example.com/signup'通过HTTPS加载，但请求了不安全的XMLHttpRequest端点' http：//myVpsIpNumber：3000/api/register '。此请求已被阻止;内容必须通过HTTPS提供。
这是我的nginx：

server {

   server_name example.com www.example.com;

    location / {
    proxy_pass http://localhost:3000;
    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection 'upgrade';
    proxy_set_header Host $host;
    proxy_cache_bypass $http_upgrade;
  }

    listen 443 ssl; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/example.com/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/example.com/privkey.pem; # managed by Certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot

}

server {
    if ($host = www.example.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot

    if ($host = example.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot

    listen 80;
    server_name example.com www.example.com;
    return 404; # managed by Certbot

}

我的快递服务器：

const express = require('express');
const cors = require('cors');

let app = express();

//routes
const user_routes = require('./routes/user.router');

// middlewares
app.use(cors());

app.use(('/'), express.static('client', {redirect: false}));
app.use('/api', user_routes);

app.get('*', function(req, res, next){
    res.sendFile(path.resolve('client/index.html'));
})

// start server
app.listen(3000, () => console.log('Server started at port : 3000'));

Angular服务：

import { HttpClient, HttpHeaders } from '@angular/common/http';

noAuthHeader = { headers: new HttpHeaders({ 'NoAuth': 'True' }) };

constructor(private http: HttpClient) {}

  postUser(user: User){
    return this.http.post('http://localhost:3000/api' + '/register', user, this.noAuthHeader);
 }

节点后端：

register: (req, res, next) => {
        let user = new User();
        user.email = req.body.email;
        user.password = req.body.password;
    
        user.save((err, doc) => {
            if (!err)
                res.send(doc);
            else {
                if (err.code == 11000)
                    res.status(422).send(['Email ya registrado']);
                else
                    return next(err);
            }
        });
    }