Laravel + Vue + Axios issue with POST method

Try to remove the trailing slash in your url.

Such as,

/api/properties/countries

Replacing that line in your original app.js would yeild this,

loadCountries: function loadCountries(total) {
axios.post('/api/properties/countries').then(function (response) {
    app.countries = response.data;
});

total = total <= this.countries.length ? total : this.countries.length;

if (total) {
    var newArr = [];
    for (i = 0; i < total; i++) {
        newArr.push(this.countries[i]);
    }
    this.countries = newArr;
}

},