How to Hide GatewayAPI Admin Menus

function plt_hide_gatewayapi_menus() {
	//Hide "Tools → Scheduled Actions".
	remove_submenu_page('tools.php', 'action-scheduler');

	//Hide "GatewayAPI".
	remove_menu_page('gatewayapi');
	//Hide "GatewayAPI → GatewayAPI".
	remove_submenu_page('gatewayapi', 'gatewayapi');
	//Hide "GatewayAPI → Campaigns".
	remove_submenu_page('gatewayapi', 'gatewayapi-campaigns');
	//Hide "GatewayAPI → Contacts".
	remove_submenu_page('gatewayapi', 'gatewayapi-contacts');
	//Hide "GatewayAPI → Shortcodes".
	remove_submenu_page('gatewayapi', 'gatewayapi-shortcodes');
	//Hide "GatewayAPI → Settings".
	remove_submenu_page('gatewayapi', 'gatewayapi-settings');
	//Hide "GatewayAPI → Migration".
	remove_submenu_page('gatewayapi', 'gatewayapi-migration');
}

add_action('admin_menu', 'plt_hide_gatewayapi_menus', 11);

Where do I put this code?