v-on:click event Vue.js to show user posts

I'm a student and I'm just getting into Vue.js so I'm still very new to it. Right now I'm making a project where I'm getting usernames from an API and when you click on the user it has to show the related post, but this is not working. When I click the button with the v-on:click event. nothing happens, not even in the console. So I hope someone can help me with my problem, I would really appreciate it.

main.js :

const app = new Vue({
el: "#app",
data: {
  users: [],
  posts: [],
},
methods: {
  Showpost(id, i) {
    fetch("https://jsonplaceholder.typicode.com/posts?userId=" + id)
    .then(response =>response.json())
    .then((data) => {
      this.posts = data;
    })
  },
},
mounted() {
  fetch("https://jsonplaceholder.typicode.com/users")
    .then(response => response.json())
    .then((data) => {
      this.users = data;
    })
},
template: `
<div>

  <td v-for="user, i in users">
    <button v-on:click="Showpost(user.id, i)" >{{ user.name }}</button>
  </td>
  <h1>{{ posts.title }}</h1>
</div>
`,
});

html :

<!DOCTYPE html>
<html lang="en">

<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css">
<title>Users</title>
</head>

<body>
<h1>Users</h1>

<div id="app">

</div>

<script src="https://unpkg.com/vue"></script>
<script src="./main.js"></script>
</body>

</html>

json users :

{
"id": 1,
"name": "Leanne Graham",
"username": "Bret",
"email": "Sincere@april.biz",
"address": {
  "street": "Kulas Light",
  "suite": "Apt. 556",
  "city": "Gwenborough",
  "zipcode": "92998-3874",
  "geo": {
    "lat": "-37.3159",
    "lng": "81.1496"
  }
},
"phone": "1-770-736-8031 x56442",
"website": "hildegard.org",
"company": {
  "name": "Romaguera-Crona",
  "catchPhrase": "Multi-layered client-server neural-net",
  "bs": "harness real-time e-markets"
}
}

json posts :

{
"userId": 1,
"id": 1,
"title": "sunt aut facere repellat provident occaecati excepturi optio reprehenderit",
"body": "quia et suscipit\nsuscipit recusandae consequuntur expedita et cum\nreprehenderit molestiae ut ut quas totam\nnostrum rerum est autem sunt rem eveniet architecto"
}

Try to create a property called post and update it on every click on a specified user by assigning this.post=data[i]:

new Vue({
  el: "#app",
  data: {
    users: [],
    posts: [],
    post: ''
  },
  methods: {
    Showpost(id, i) {
      fetch("https://jsonplaceholder.typicode.com/posts?userId=" + id)
        .then(response => response.json())
        .then((data) => {
          this.post = data[i];

        })
    },
  },
  mounted() {
    fetch("https://jsonplaceholder.typicode.com/users")
      .then(response => response.json())
      .then((data) => {
        this.users = data;
      })
  },
  template: `
<div class="flex">

  <div v-for="user, i in users">
    <button class="btn" v-on:click="Showpost(user.id, i)" >{{ user.name }}</button>
  </div>
  <h1>{{ post.title }}</h1>
</div>
`,
});

.flex{
display:flex;
flex-wrap:wrap;
}

<!DOCTYPE html>
<html>

<head>
  <meta name="description" content="Vue.delete">
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>JS Bin</title>
  <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css" integrity="sha384-MCw98/SFnGE8fJT3GXwEOngsV7Zt27NXFoaoApmYm81iuXoPkFOJwJ8ERdknLPMO" crossorigin="anonymous">
  <script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.2.1/vue.min.js"></script>
</head>

<body>
  <div id="app">

  </div>