How to add settings subpage from a plugin to a settings page created in theme?

Question

I'm using add_menu_page(...) from a custom theme and I want to add subpages to that menu with add_submenu_page(...) . If I try to do it from the theme it works as expected but when I try the same from a plugin it just does nothing.

I thought it could be possible that the plugin would be trying to add the submenu page before the menu did even exist, so I wrapped the code in within a function and used add_action(...) from the plugin using a custom action hook created in the place where I wanted the code to execute (in the exact line it worked in the theme) with do_action(...).

The example code would be this:

(theme)

function wvdh_add_admin_page(){
    // The next 2 lines work fine
    add_menu_page( 'WVDH - Settings','WVDH', 'manage_options', 'wdvh-startpoint', 'render_page', 'dashicons-admin-network', '109');
    add_submenu_page( 'wdvh-startpoint', 'page-title', 'menu-title', 'manage_options', 'menu-slug', 'render_page'  );
    // The next line does nothing
    do_action('wvdh-menu');
}
add_action('admin_menu', 'wvdh_add_admin_page');

function render_page(){
    echo '<h1>Test</h1>';
}

(plugin)

add_action('admin_menu', 'wvdh_create_menu');

function wvdh_create_menu() {
    add_action('wvdh-menu', 'new_subpage');
}

function new_subpage(){
    add_submenu_page( 'wvdh-startpoint', 'page-from-plugin', 'menu-from-plugin', 'manage_options', 'plugin-slug', 'wvdh_settings_page' );
}

function wvdh_settings_page() {
    echo '<h1>Test from-plugin</h1>';
}

Answer 1

This is just a typo

Wrong

//wvdh-startpoint
add_submenu_page( 'wvdh-startpoint', 'page-from-plugin', 'menu-from-plugin', 'manage_options', 'plugin-slug', 'wvdh_settings_page' );

Correct

//wdvh-startpoint
add_submenu_page( 'wdvh-startpoint', 'page-from-plugin', 'menu-from-plugin', 'manage_options', 'plugin-slug', 'wvdh_settings_page' );