Contact Form: 404 Not Found when submitting

I’m using the contact form block to implement a simple Contact Us like page. The plugin itself works fine (no connection errors or other issues), but when I try to submit form by pressing Submit button I receive Page Not Found error.

Already tried to disable all other plugins and turn on the default Twenty Twenty-Four theme.

Environment:

• Windows IIS with configured rewrite rule
• PHP 8.3.1
• Cloudflare DNS with tunneling
• WordPress 6.4.3
• Jetpack 13.1.3

Request output inside the browser:

Request Method: POST
Status Code: 404 Not Found

WordPress log file:

PHP Warning:  Attempt to read property "ID" on null in C:\inetpub\wwwroot\wordpress\wp-content\plugins\jetpack\jetpack_vendor\automattic\jetpack-forms\src\contact-form\class-contact-form.php on line 1038
PHP Stack trace:
PHP   1. {main}() C:\inetpub\wwwroot\index.php:0
PHP   2. require() C:\inetpub\wwwroot\index.php:17
PHP   3. require_once() C:\inetpub\wwwroot\wordpress\wp-blog-header.php:19
PHP   4. do_action($hook_name="template_redirect") C:\inetpub\wwwroot\wordpress\wp-includes\template-loader.php:13
PHP   5. WP_Hook->do_action($args = [0 => '']) C:\inetpub\wwwroot\wordpress\wp-includes\plugin.php:517
PHP   6. WP_Hook->apply_filters($value="", $args = [0 => '']) C:\inetpub\wwwroot\wordpress\wp-includes\class-wp-hook.php:348
PHP   7. Automattic\Jetpack\Forms\ContactForm\Contact_Form_Plugin->process_form_submission('') C:\inetpub\wwwroot\wordpress\wp-includes\class-wp-hook.php:324
PHP   8. Automattic\Jetpack\Forms\ContactForm\Contact_Form->process_submission() C:\inetpub\wwwroot\wordpress\wp-content\plugins\jetpack\jetpack_vendor\automattic\jetpack-forms\src\contact-form\class-contact-form-plugin.php:734

The page I need help with: [log in to see the link]