Why is this JSON error popping up?

Question

JavaScript

Why does this error pop up?

Error in this line, as I understand it

"use strict"
document.addEventListener('DOMContentLoaded', function () {
    const form = document.getElementById('form');
    form.addEventListener('submit', formSend);

    async function formSend(e) {
        e.preventDefault();

        let error = formValidate(form);

        let formData = new FormData(form);
        

        if(error === 0){
            form.classList.add('sending');
            let response = await fetch('sendmail.php', {
                method: 'POST',
                body: formData
            })
            if (response.ok){
                let result = await response.json();
                alert(result.message);
                formPreview.innerHTML = '';
                form.reset();
            }else{
                alert('Ошибка')
            }

        }else{
            alert('Заполните обязательные поля')
        }
    }


    function formValidate(form) {
        let error = 0;
        let formReq  = document.querySelectorAll('.req');
        for (let index = 0; index < formReq.length; index++) {
            const input = formReq[index];
            formRemoveError(input);

            if(input.classList.contains('email')){
                if(emailTest(input)){
                    formAddError(input)
                    error++;
                }

            }else if(input.getAttribute("type") === "checkbox" && input.checked === false){
                formAddError(input);
                error++;
            }else{
                if(input.value === ''){
                    formAddError(input);
                    error++;
                }
            }
            
        }

        return error;
    }

    function formAddError(input) {
        input.parentElement.classList.add('error');
        input.classList.add('error');
    }

    function formRemoveError(input) {
        input.parentElement.classList.remove('error');
        input.classList.remove('error');
    }

    function emailTest(input) {
         return !/^\w+([\.-]?\w+)*@\w+([\.-]?\w+)*(\.\w{2,8})+$/.test(input.value);
        
    }

})

Answer 1

Because not JSON comes from the server, but HTML or XML.