AJAX POST request not working with XMLHttpRequest in Laravel - laravel

Question

I'm using XMLHttpRequest to avoid using JQuery and I wanna make an Ajax request to delete an object but I keep getting redirected back and getting FOUND (302) HTTP errors.
This is my code:
function deleteGuia(urlToSend) {
var borra = confirm('¿Está seguro de borrar la guía?');
if (!borra) {
return;
}
var req = new XMLHttpRequest();
var csrfToken = document.querySelector('meta[name="csrf-token"]').content;
req.open("POST", urlToSend, true);
req.setRequestHeader('X-CSRF-TOKEN', csrfToken);
req.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded; charset=UTF-8');
req.onreadystatechange = function () {
if (req.readyState === 4) {
if (this.readyState === this.DONE) {
console.log(this.responseURL);
}
if (req.status != 200) {
var msg = JSON.parse(req.response);
alert(msg.error);
} else {
alert('Exitoso');
}
}
}
var data = new FormData();
var guia = "{{$guia ?? ''}}";
var estado = "{{$tipo ?? ''}}";
data.append("guia", guia);
data.append("tipo", estado);
req.send(data);
}
</script>
This one's the controller function:
public function eliminarGuia(Request $request) {
$request->validate([
'guia' => 'required|numeric',
'tipo' => 'required'
]);
$guia = (int)$request->input('guia');
$tipo = $request->input('tipo');
\Log::info('Guia' . $guia . ' Tipo: '. $tipo);
if (strtoupper($tipo) === 'ENTREGA'){
$borra_guia = Guia::where('guia', $guia)->where('estado', $tipo)->delete();
$borra_ciclos = Device::where('guia_recepcion', $guia)->delete();
if(!$borra_guia) {
return response(400)->json(['error', 'La guía no se encontró.']);
}
} else if (strtoupper($tipo) === 'REVERSA') {
$borra_guia = Guia::where('guia', $guia)->where('estado', $tipo)->delete();
$devices = Device::where('guia_reversa', $guia)->get();
if (!$borra_guia){
return response(400)->json(['error', 'La guía no se encontró.']);
}
foreach($devices as $device)
{
if (!$device->fecha_recepcion) {
$device->delete();
} else {
$device->guia_reversa = 0;
$device->fecha_reversa = null;
$device->save();
}
}
} else {
return response(400)->json(['error', 'La guía no se encontró.']);
}
return response(200);
}
web.php
Route::post('borrar_guia', 'VistasController#eliminarGuia')->name('borrar_guia');
There's no redirection at all. Why might that be happening? I don't know what else to add. The controller should return a 200 code when it delets an existing object in the database but it's getting a 200 from the redirection.