How to pass json to server using Fetch in Vue.cli?

Question

Vue.js

I created a json file on the server, I read data from it normally and fill it in the required fields in the app, but I can’t transfer data to this file.
I develop through localhost: 8080 Vue.cli.
2 questions in this regard:
1. Do I need an Apachi server to transfer and write json data to a file,
or
2. Is it enough to just have an index.php config in a folder on the server?

If option 2, what should it be? (I don’t understand in php)

Below is the code with which I am trying to transfer data to a file, where contacts is a link to the data array from the completed form in the form:

methods: {
            saveContact(formData) {
                     let contacts = this.userData.push (formData);
                     
                     var requestURL = "./data/user_data.json";
                     let data = JSON.stringify(contacts);
                     const fetchOptions = {
                         credentials: "include",
                         method: "POST",
                         headers: { "Content-Type": "application/json", },
                         body: data,
                     };

                     fetch(requestURL, fetchOptions)
                     .then((response) => response.json())
                     .catch((error) => {
                              console.log( "Возникла проблема с вашим fetch запросом: ",  error.message );
                      });
}