Laravel 8 on shared hosting server in subfolder

I am trying to move my local laravel 8 app to a shared hosting server. The server is in the address 'www.nameofsite.com'.

I need to put the application inside 'www.nameofsite.com/myapp'

I don't have public_html inside the 'www.nameofsite.com'.

Using FTP I created a folder called myapp inside the folder www. nameofsite. com; then I copied the local version of myapp inside this live myapp folder. I moved public folder to be at the same level as the application folder. At the moment i have the app setup in the following way:

                                           |--- css, js, index.php, etc...
www.nameofsite--->myapp--->|
                                           |--- myapp-> app, bootstrap, etc.....

I modified the index.php setting:

if (file_exists(__DIR__.'/myapp/storage/framework/maintenance.php')) {
    require __DIR__.'/myapp/storage/framework/maintenance.php';
}

and I repeated the same operation for vendor and bootstrap in the index.php.

Now the problem: I launch the site going to 'www.nameofsite.com/myapp', the laravel 8 auth starts and it brings me to:

www.nameofsite.com/myapp/items/create

that is the form of creation of the item. As soon as I push the button SAVE of the form, I get the "Not Found The requested URL was not found on this server".

And the URL appearing in the address bar is:

www.nameofsite.com/items

(it lost the /myapp/ part)

In the web.php file I have a normal setup for the Items routing:

Route::post('/items','App\Http\Controllers\ItemsController@store')->middleware('auth','isAdmin');

and in the view i have:

<form method="POST" action="/items" class="mt-5">
            @csrf
  . .....

The .htaccess which is at the same level of index.php is the following:

Options -MultiViews

RewriteEngine On

RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)/$ / [L,R=301]

RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^ index.php [L]

RewriteCond %{HTTP:Authorization} .
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
</IfModule>

I can't understand why it behaves like this or why it jumps back to the "master" parent folder ('www.nameofthesite.com') when I do the POST action