App works locally but errors when hosted?

I have this api with fetch that is taking the data of a form, with the formdata object optengo the data of said form built in html, then they are sent to the server, a php file that processes the data sent from javascript, in php the data are stored in a database and sends a response to the client, the problem I have is that in local I have tried and everything goes great, but when I go to a paid hosting to try my application optengo a

let formulario = document.getElementById('formulario');

formulario.addEventListener('submit', function (e) {
    e.preventDefault();

    const datos = new FormData(formulario);

    fetch('./includes/add.php', {
        method: 'POST',
        headers: {
            'Content-Type': 'application/json;charset=utf-8'
        },
        mode: 'cors',
        body: datos
    })
        .then(res => res.json())
        .then(data => {
            console.log(data);
            if (data == 'respuesta') {
                Swal.fire({
                    icon: 'success',
                    title: 'mensaje enviado',
                    showConfirmButton: true,
                    timer: 1500
                })
                formulario.reset();

            } else if (data == "error") {
                Swal.fire({
                    icon: 'error',
                    title: 'mensaje no enviado',
                    showConfirmButton: true,
                    timer: 1500
                })
                formulario.reset()
            }
        })
})

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