Using a trait in all controllers

However none of my controllers could find the trait.

How are you using the trait inside your controllers?

Inside say the update method:

return redirect(route('customer.index'))->with(Alert::success('Success message here!'));

Is it because I'm calling static methods on the trait?

This is what my base Controller class looks like.

<?php

namespace App\Http\Controllers;

use App\Traits\Alert;
use Illuminate\Foundation\Bus\DispatchesJobs;
use Illuminate\Routing\Controller as BaseController;
use Illuminate\Foundation\Validation\ValidatesRequests;
use Illuminate\Foundation\Auth\Access\AuthorizesRequests;

class Controller extends BaseController
{
    use Alert, AuthorizesRequests, DispatchesJobs, ValidatesRequests;
}

This works using self::success() instead of Alert::success() -

return redirect(route('customer.index'))->with(self::success('Success message here!'));

Must be bad practice to use static methods on a trait from a parent class maybe?

This isn't how inheritance works. If you want to use it in your other controllers, you need to import it in them. And by the looks of it, your Alert trait would be better suited as some kind of service class.