https://stackoverflow.com/questions/53020833/count-parameter-must-be-an-array-or-an-object-that-implements-countable-in-lar

Nope.

You should create a custom plugin for this.

Learn more on http://learn.elgg.org/en/3.x/guides/routing.html

But there's Static plugin that lets you use custom pages with your URI.

Static plugin is ok - great!

This is a bug. PR is opened already.

Until this issue is fixed you can temporarily do the following:

In the file:

mod\groups\start.php

Under on:

function _groups_title_menu(\Elgg\Hook $hook) {

Comment this part (lines 896-902):

/*

$result[] = \ElggMenuItem::factory([
      'name' => 'groups:invite',
      'icon' => 'user-plus',
      'href' => elgg_generate_entity_url($group, 'invite'),
      'text' => elgg_echo('groups:invite'),
      'link_class' => 'elgg-button elgg-button-action',
]);

*/

Thanks a lot, Nikolai! It works...