Laravel package route can't find controller class - php

Question

I have created a Laravel package using the guidelines of https://laravelpackage.com/.
My package name is Company/FirstPackage.
It resides in the WebSite/packages folder of a host Laravel application.
In it I have created a controller in src/Http/Controllers:
namespace Company\FirstPackage\Controllers;
class FirstController extends Illuminate\Routing\Controller {
public function getName() {
return response()->json('hi, this is name');
}
}
And I have created a simple api.php file in the WebSite/packages/Company/FirstPackage/route directory and in it, I have this route:
use Illuminate\Support\Facades\Route;
Route::get('/name', [Company\FirstPackage\Controllers\FirstController:class, 'getName']);
Route::get('/testRoute', function() { return 'route is working'; });
The 127.0.0.1:8000/testRoute works as expected. But when I go to 127.0.0.0:8000/name I get this error:
Illuminate\Contracts\Container\BindingResolutionException Target class
[Company\FirstPackage\Controllers\FirstController] does not exist.
I have tried all suggestions in this link:
Add the namespace back manually so you can use it as you did in
Laravel 7.x and before
Use the full namespace in your route files when using the
string-syntax
Use the action syntax (recommended)
But non of them worked.
How should I fix this bug?
Update: Part of the content of the composer.json is as follow:
"autoload": {
"psr-4": {
"Company\\FirstPackage\\": "src/"
}
},
"extra": {
"laravel": {
"providers": [
"Company\\FirstPackage\\FirstPackageServiceProvider"
]
}
}