Can't upload image via submitting custom post from frontend

I have an issue with submitting custom post from frontend with image. I have a form with post title, description and image, that should be featured image of the post. So when user submitting post, it actually creates with title and description, but without image, even in media library the image doesn’t appear. Here is my form:

<form id="_themename-advert-create-form" method="post" enctype="multipart/form-data">
    <?php wp_nonce_field('_themename_submit_advert_action','__themename_submit_advert_nonce'); ?>
    <input type="hidden" name="_themename-advert-create-check" value="1" />
    
    <label for="_themename-advert-create-title">Title</label>
    <input id="_themename-advert-create-title" type="text" name="_themename-advert-create-title" />

    <label for="_themename-advert-create-content">Sample Content</label>
    <textarea id="_themename-advert-create-content" rows="8" name="_themename-advert-create-content"></textarea>

    <label for="_themename-advert-create-image">Upload Post Image</label>
    <input type="file" id="_themename-advert-create-image" name="_themename-advert-create-image" />

    <input type="submit" id="_themename-advert-create-submit" value="SUBMIT" name="_themename-advert-create-submit" />

</form>

Here is my function that creates custom post:

add_action('init', '_themename_create_new_post');
function _themename_create_new_post(){
    
    if('POST' == $_SERVER['REQUEST_METHOD'] && isset($_POST['_themename-advert-create-check']) && wp_verify_nonce( $_POST['__themename_submit_advert_nonce'], '_themename_submit_advert_action')) {
        $current_user = wp_get_current_user();
        $user_id = $current_user->ID;

        $new_post_title = sanitize_text_field($_POST['_themename-advert-create-title']);
        $new_post_content = sanitize_textarea_field($_POST['_themename-advert-create-content']);

        $new_post = array();
        $new_post['post_author'] = $user_id;
        $new_post['post_title'] = $new_post_title;
        $new_post['post_content'] = $new_post_content;
        $new_post['post_status'] = 'pending';
        $new_post['post_name'] = 'pending';
        $new_post['post_type'] = 'jana_usa';

        $post_success = wp_insert_post($new_post);
        
        if ( $_FILES ) { 
            $files = $_FILES["_themename-advert-create-image"];  
            foreach ($files['name'] as $key => $value) {
                if ($files['name'][$key]) {
                    $file = array( 
                        'name' => $files['name'][$key],
                        'type' => $files['type'][$key], 
                        'tmp_name' => $files['tmp_name'][$key], 
                        'error' => $files['error'][$key],
                        'size' => $files['size'][$key]
                    );
                    $_FILES = array ("_themename-advert-create-image" => $file);
                    foreach ($_FILES as $file => $array) {              
                        // $newupload = frontend_handle_attachment( $file, $post_success );
                        if ($_FILES[$file]['error'] !== UPLOAD_ERR_OK) __return_false();

                        require_once(ABSPATH . "wp-admin" . '/includes/image.php');
                        require_once(ABSPATH . "wp-admin" . '/includes/file.php');
                        require_once(ABSPATH . "wp-admin" . '/includes/media.php');

                        $attach_id = media_handle_upload( $file, $post_success );

                        // Set featured image 
                        set_post_thumbnail($post_success, $attach_id);
                    }
                }
            }
        }

    }

}

After submittin I’m getting an error Warning: Invalid argument supplied for foreach() in ... on line 43. This line:

foreach ($files['name'] as $key => $value) { ...

I can’t find how to solve it. What am I doing wrong?

<input type="file" id="_themename-advert-create-image" name="_themename-advert-create-image" />

<input type="file" id="_themename-advert-create-image" name="_themename-advert-create-image[]" />