Buefy this.$toast is undefined error

App.vue

<template>
  <div id="app">
    <img src="./assets/logo.png">
    <router-view/>
    <button class="button" @click="logout">Test Toast</button>
  </div>
</template>

<script>
export default {
  name: 'App',
  methods:{
    logout: ()=>{this.$toast.open({message:'Erro:'+err.message,type:'is-danger'})}
  }
}
</script>

<style>
#app {
  font-family: 'Avenir', Helvetica, Arial, sans-serif;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-align: center;
  color: #2c3e50;
  margin-top: 60px;
}
</style>