Capability to change settings

Referring to https://ww.wp.xz.cn/support/topic/add-user-capability-to-manage-bookings-settings?replies=2 – I would need that, too. This is, how far I came:

$sap->add_page(
	'submenu',
	array(
		'id'            => 'rtb-settings',
		'title'         => __( 'Settings', RTB_TEXTDOMAIN ),
		'menu_title'    => __( 'Settings', RTB_TEXTDOMAIN ),
		'parent_menu'	=> 'rtb-bookings',
		'description'   => '',
		'capability'    => 'manage_options',
		'default_tab'   => 'rtb-general',
	)
);

Changing “manage_options” to “custom_manage_options”, then adding at user role editor a capability “custom_manage_options”.

That took me as far as enabling people with the “custom”-Capability to SEE the settings. But if they are trying to change them, the response is “trying to cheat, eh?”

Any advise?

https://ww.wp.xz.cn/plugins/restaurant-reservations/