How to upload images via REST API

I’m uploading images via the rest-api. So far I’m able to upload the file to the directory, but in the admin panel I see an empty image, because the image source is set to “default.png/jpeg”. Why isn’t using the file name?

$json           = $request->get_file_params();
    $json_encode    = json_encode($json);
    $files          = json_decode($json_encode, true);
    $upload_dir     = wp_upload_dir();
    $file_name      = $files['image']['name'];
    $file_to_upload = $upload_dir['path']."/".$file_name;

    $file_array = array('name' => $file_name, 'type' => $files['image']['type'], 'size' => $files['image']['size'], 'tmp_name' => $files['image']['tmp_name'] );

    $filetype = wp_check_filetype( basename( $file_to_upload ), null );

    $attachment = array(
        'guid'           => $upload_dir['url'] . '/' . basename( $file_to_upload ),
        'post_mime_type' => $filetype['type'],
        'post_title'     => preg_replace( '/\.[^.]+$/', '', basename( $file_to_upload ) ),
        'post_content'   => '',
        'post_status'    => 'inherit'
    );

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

    $uploadedfile = $request->get_file_params();
    $upload_overrides = array( 'test_form' => false );

    $movefile  = wp_handle_upload( $file_array, $upload_overrides );
    $attach_id = wp_insert_attachment($attachment, $movefile['file'], 0);

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