copy main site to subdomain error

I'm trying to copy my main site to a subdomian on shared hosting following this link:

http://novate.co.uk/deploy-laravel-5-on-shared-hosting-from-heart-internet/

I created a subdomain called:

testhighland under public_html

I created a folder called: testhighland under a folder called: applications (that's where my main site sits as well).

I copied everything besides the public folder from my applications/mainsite to applications/testhighland.

I copied everything from the public folder from applications/mainsite to the public_html/testhighland folder.

I changed these lines in public_html/testhighland/index.php:

//require __DIR__.'/../../applications/mainsite/bootstrap/autoload.php';
require __DIR__.'../../../applications/testhighland/bootstrap/autoload.php';

//$app = require_once __DIR__.'/../../applications/mainsite/bootstrap/app.php';
$app = require_once __DIR__.'/../../../applications/testhighland/bootstrap/app.php';

Trying to run the testhighland domain I don't get the styles. The link to css/app.css does not work and I get this error:

Oh Snap! We can't find what you are looking for...

I tried to change the env file:

APP_URL=https://testhighland.mainsite.co.za

and the config/app.php:

'url' => env('APP_URL', 'https://testhighland.highlandcoffeeroastery'),

Then I get the same error but it's worse, because the data of the page does not diaplay either not just the styles

I moved all the public files and folders into: public_html/testhighland/public

Didn't help either

Can anyone please help?