Trouble with TenderApp link in menu

I’m using the Multipass plugin to create an SSO login link to TenderApp.

Works fine.

Except I’m trying to add a link to the TenderApp forum in the menu.

In the header.php file of the theme I’m doing the following:

function my_forum_wrap() {
				if (memb_is_loggedin()) {
					$url =  multipass();
					$link =  "<a href='".$url."' target='_blank'>Forum</a>";
					$wrap  = '<ul id="%1$s" class="%2$s">';
					$wrap .= '%3$s';
					$wrap .= "<li class='menu-item'>".$link."</li></ul>";
					return $wrap;
				}
			}
				wp_nav_menu(array(
					'theme_location' => 'topbar',
					'menu_id' => 'topbar-menu',
					'depth' => defined('SO_IS_PREMIUM') ? 2 : 1,
					'fallback_cb' => 'pitch_fallback_nav',
					'walker' => new Pitch_Walker_Nav_Menu,
					'items_wrap' => my_forum_wrap(),
				));

When I run it like this it breaks the function and no menu is outputted. If I just echo multipass() it spits out the URL on the screen just fine. If i just hardcode a random URL in there, it works fine. I’ve done a var_dump of what multipass() is returning and it’s just a string URL that looks like this: https://esupport-forum.tenderapp.com?sso=nWxbYLxasdfS1ILXQx%2B9jKTUiit9qlR5hY%2FZFm8gD5hHgfstHi0Wk7r4MglfCY27esUhn00JkaszuD6bfdsB9rMMcSPG%2FhOasdX8HowBnZv8bczooWRQvJ4Qbs2z79L4ZpmWsGoW6kas7S4cp3jsq7CuMFQTHdVnZfd1vPDs2CsWp90ispQgfdrQoh3z35yTo%3D I can’t understand why putting the URL into the wp_nav_menu function breaks it.

Any ideas?