[Vuejs]-Laravel, Vue fetch returns nothing but there is data in console

1. Your method doesn’t return anything so there’s nothing to render.
2. Your method is asynchronous so you could not return any value even if you wanted to.

TL;DR try to avoid using methods in your templates and instead, load data into your data properties. For example

<template>
  <div id="container">
    <span v-if="municipality">{{ municipality }}</span>
    <span v-else>Loading...</span> <!-- 👈 totally optional -->
  </div>
</template>

data () {
  return { municipality: null }
},
methods: {
  loadMunicipality (id) {
    return fetch(`api/biodidb/get_municipality_name_by_id/${id}`)
        .then(res => res.json())
        .then(obj => obj.Municipality)
  }
},
created () {
  this.loadMunicipality(12).then(municipality => {
    this.municipality = municipality
  }).catch(err => {
    console.error(err)
  })
}