If you encounter this problem with Apache but the app doesn’t have any problem while running directly.

php artisan serve --host 0.0.0.0

Then you should check apache log:

cd /var/log/apache2/
cat error.log

If you see the error like this, see whether you have upgraded PHP.

[:error] PHP Parse error: syntax error, unexpected '=' in /xxx/Arr.php on line 384

If it’s your case, you should do the following procedures since Apache doesn’t automatically use the new PHP.

sudo a2dismod php7.0
sudo a2enmod php7.3
sudo systemctl restart apache2

Check the url again 🙂