Use this code example to turn off the landing page URLs in API script frames for any form.

add_filter( 'frm_api_iframe_use_landing_page_url', '__return_false' );

Use this code example to turn off the landing page URLs in API script frames for a specific form ID.

add_filter('frm_api_iframe_use_landing_page_url', 'disable_api_iframe_use_landing_page_url' , 10, 2);
function disable_api_iframe_use_landing_page_url( $use_landing_page_url, $form_id ) {
	$target_form_id = 1401; //Replace 1401 with the ID of your form
	if ( $target_form_id === $form_id ) {
		$use_landing_page_url = false;
	}
	return $use_landing_page_url;
}