I have a WordPress website with a newsletter subscription code written in JavaScript and PHP. Everything works fine on localhost, but when I upload the website to hosting, the page freezes after clicking the button, and after a while an error message appears in the console: curl: (28) Failed to connect to (my api url) port 443 after 128807 ms: Connection timed out

Javascript code

 document.getElementById('submit_newsletter').addEventListener('click', function (e) {
        e.preventDefault();
        
        var email = document.getElementById('KPGH_newsletter_email').value;
        var nonce = document.getElementById('KPGH_message_nonce').value;
        var validationError = false;
        
        if (!validateEmail(email)) {
            document.getElementById('KPGH_email_err').style.display = 'block';
            validationError = true;
        } else {
            document.getElementById('KPGH_email_err').style.display = 'none';
        }
    
        if (validationError) {
            return;
        }
    
        var message = new FormData();
        message.append('action', 'KPGH_newsletter_form');
        message.append('KPGH_newsletter_email', email);
        message.append('KPGH_message_nonce', nonce);
    
        console.log("Sending AJAX request to: " + ajax_url);
        console.log("FormData: ", message);
    
        var xhr = new XMLHttpRequest();
        xhr.open('POST', ajax_url, true);
        xhr.responseType = 'json';
    
        xhr.onload = function () {
            if (xhr.status >= 200 && xhr.status < 400) {
                console.log("AJAX success response: ", xhr.response);
                if (xhr.response.success) {
                    document.getElementById('KPGH_newsletter_succes').innerHTML = xhr.response.data;
                    document.getElementById('KPGH_newsletter_succes').style.display = 'block';
                    setTimeout(function () {
                        document.getElementById('KPGH_newsletter_succes').style.display = 'none';
                    }, 4500);
                } else {
                    document.getElementById('KPGH_newsletter_error').innerHTML = xhr.response.data;
                    document.getElementById('KPGH_newsletter_error').style.display = 'block';
                    setTimeout(function () {
                        document.getElementById('KPGH_newsletter_error').style.display = 'none';
                    }, 4500);
                }
            } else {
                console.log("AJAX error response: ", xhr.response);
                document.getElementById('KPGH_newsletter_error').innerHTML = xhr.statusText;
                document.getElementById('KPGH_newsletter_error').style.display = 'block';
                setTimeout(function () {
                    document.getElementById('KPGH_newsletter_error').style.display = 'none';
                }, 4500);
            }
        };
    
        xhr.onerror = function () {
            console.log("AJAX request failed");
            document.getElementById('KPGH_newsletter_error').innerHTML = "Request failed";
            document.getElementById('KPGH_newsletter_error').style.display = 'block';
            setTimeout(function () {
                document.getElementById('KPGH_newsletter_error').style.display = 'none';
            }, 4500);
        };
    
        xhr.send(message);
    });
    
    function validateEmail(email) {
        var re = /^(([^<>()[]\.,;:s@"]+(.[^<>()[]\.,;:s@"]+)*)|(".+"))@(([[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}])|(([a-zA-Z-0-9]+.)+[a-zA-Z]{2,}))$/;
        return re.test(String(email).toLowerCase());
    }

PHP Code (functions.php)

if (!function_exists('KPGH_newsletter_form')) {
    function KPGH_newsletter_form() {
        // Sprawdź czy nonce jest ustawione
        if (!isset($_POST['KPGH_message_nonce']) || !wp_verify_nonce($_POST['KPGH_message_nonce'], 'KPGH-ajax-message-submit')) {
            error_log('Nonce verification failed');
            wp_send_json_error('Nonce verification failed');
        }

        $url = 'https://xxxxxxx/api/2/auth/xxxxxxxxxx';
        $login = 'xxxxxxxx';
        $password = 'xxxxxx';
        $headers = array(
            'ACCEPT: application/x-www-form-urlencoded',
            'USER_AGENT: xxxxx'
        );

        // Wysyłanie żądania uwierzytelniającego
        $curl = curl_init();
        curl_setopt_array($curl, array(
            CURLOPT_URL => $url,
            CURLOPT_HTTPHEADER => $headers,
            CURLOPT_USERPWD => $login . ':' . $password,
            CURLOPT_RETURNTRANSFER => true,
            CURLOPT_SSL_VERIFYPEER => false,
            CURLOPT_SSL_VERIFYHOST => false,
        ));
        
        $tokenResponse = curl_exec($curl);
        if ($tokenResponse === false) {
            error_log('Curl error: ' . curl_error($curl));
            curl_close($curl);
            wp_send_json_error('Curl error: ' . curl_error($curl));
        }
        
        $tokenData = json_decode($tokenResponse);
        if (json_last_error() !== JSON_ERROR_NONE || !isset($tokenData->data)) {
            error_log('Token not received or json decode error: ' . json_last_error_msg());
            curl_close($curl);
            wp_send_json_error('Authentication failed');
        }
        
        $token = $tokenData->data;
        error_log('Token received: ' . $token);
        curl_close($curl);
        
        // Przygotowanie danych kontaktowych
        $contact = array(
            'contact' => array(
                array(
                    'email' => sanitize_email($_POST['KPGH_newsletter_email']),
                    'category' => array('26' => '1'),
                    'agreement' => array('1' => '1'),
                    'contactAccess' => array('ID_CONTACT_ACCESS' => 1),
                    'source' => array(
                        'utm_campaign' => 'CAMPAIGN_NAME',
                        'utm_content' => 'CAMPAIGN_CONTENT',
                        'utm_medium' => 'CAMPAIGN_MEDIUM',
                        'utm_source' => 'CAMPAIGN_SOURCE',
                        'utm_term' => 'CAMPAIGN_TERM',
                    )
                )
            )
        );

        // Wysyłanie danych kontaktowych
        $url = 'xxxxxxxx/api/2/contact/';
        $headers[] = 'IPRESSO_TOKEN: ' . $token;
        
        $curl = curl_init();
        curl_setopt_array($curl, array(
            CURLOPT_URL => $url,
            CURLOPT_POST => true,
            CURLOPT_POSTFIELDS => http_build_query($contact),
            CURLOPT_HTTPHEADER => $headers,
            CURLOPT_RETURNTRANSFER => true,
            CURLOPT_SSL_VERIFYPEER => false,
            CURLOPT_SSL_VERIFYHOST => false,
        ));
        
        $contactResponse = curl_exec($curl);
        if ($contactResponse === false) {
            error_log('Curl error: ' . curl_error($curl));
            curl_close($curl);
            wp_send_json_error('Curl error: ' . curl_error($curl));
        }
        
        $contactData = json_decode($contactResponse);
        if (json_last_error() !== JSON_ERROR_NONE || !isset($contactData->data->contact)) {
            error_log('Contact not received or json decode error: ' . json_last_error_msg());
            curl_close($curl);
            wp_send_json_error('Adding contact failed');
        }
        
        $code = null;
        foreach ($contactData->data->contact as $child) {
            $code = $child->code;
        }

        error_log('Response code: ' . $code);
        curl_close($curl);

        switch ($code) {
            case 303:
            case 302:
                wp_send_json_success('Podany adres już jest w naszej bazie danych.');
                break;
            case 200:
            case 201:
                wp_send_json_success('Twoja email został dodany do naszej bazy. Dziękujemy!');
                break;
            default:
                wp_send_json_error('Przepraszamy, nie udało się dodać twojego adresu email do naszej bazy');
        }
    }
}

add_action('wp_ajax_KPGH_newsletter_form', 'KPGH_newsletter_form');
add_action('wp_ajax_nopriv_KPGH_newsletter_form', 'KPGH_newsletter_form');

On localhost it works great, here is the video of the newsletter fully working:
https://streamable.com/7wkvt2

So could it be a hosting issue?
error

I tried disabling other plugins, but unfortunately it doesn’t help.