I have a custom app, and I set up a custom menu tab in the ACP in my development environment. My acpmenu.json file looks like this:

{
    "machines": {
        "versions": {
            "tab": "posts",
            "controller": "versions",
            "do": "",
            "restriction": null
        }
    },
    "directory": {
        "settings": {
            "tab": "posts",
            "controller": "settings",
            "do": "",
            "restriction": null
        }
    }
}

and in my lang.php file, I have

'menutab__posts' => "Posts",
'menutab__posts_icon' => "laptop",

Works perfectly in my dev environment. I build the app, install on the customer site... menu tab does not show up. Suggestions? Ideas? I've been banging my head over this one for 2 days now. I've tried uninstalling and re-installing, rebuilding... nothing works.  

Are there restrictions on the admin account? If there are restrictions pre-set on an account or group, rather than blanketly having all permissions, then the new application will not be automatically inherited, and will need to be set manually.

EDIT: Note, restrictions can be applied at both the module and application level. So if the administrator does not have access to the application at all, in their restrictions, then it won't show.

Just now, Ryan Ashbrook said:

Are there restrictions on the admin account? If there are restrictions pre-set on an account or group, rather than blanketly having all permissions, then the new application will not be automatically inherited, and will need to be set manually.

I'm an Administrator. No secondary groups. No restrictions.

26 minutes ago, HeadStand said:

I'm an Administrator. No secondary groups. No restrictions.

Are you certain there are no restrictions? What is the contents of core_admin_permission_rows? An asterisk would indicate all permissions, and inherit from new applications, and a JSON object would indicate specific permissions, with no inheritance for new applications (even if every single permission is selected).

Restrictions are the only thing, off the top of my head without seeing the site, that would cause a menu tab to not show.

Just now, Ryan Ashbrook said:

Are you certain there are no restrictions? What is the contents of core_admin_permission_rows? An asterisk would indicate all permissions, and inherit from new applications, and a JSON object would indicate specific permissions, with no inheritance for new applications (even if every single permission is selected).

It's an asterisk.

Feeling incredibly stupid right now. My Application::canAccess method had a permission check in there to check group permissions. I added

if( \IPS\Dispatcher::hasInstance() && \IPS\Dispatcher::i()->controllerLocation == 'admin' )
{
    return true;
}

and now it works. ** facepalm **