No, it wasn't correctly pasted. I have edited my warning description.
Do you have any other ideas?

• you're using Apache webserver?
• mod_rewrite is enabled (probably yes otherwise Elgg won't work)
• if, in your browser, you go to http://yoursite.com/vendor/autoload.php what kind of response do you get (check your browser developers info (F12) then the network tab)

The htaccess hardening isn't something that needs to be active, it just helps with the protection of your website.

Of course I can understand that you wish to do the best you can to secure your site.

I can't think of more things you could check. Maybe Google "apache rewritecond not working" for suggestions???

Yes, I am using an apache webserver. mod_rewrite is enabled. If I go to http://yoursite.com/vendor/autoload.php the following 403 Error occures:

1. Request-URL:
   http://192.168.56.102/vendor/autoload.php
2. Request method:
   GET
3. Statuscode:
   403 Forbidden
4. Remote-Address:
   192.168.56.102:80

1 - Check the read/write permissions on this folder

2 - Check the .htaccess rules on access to this folder

looks like you don't have the PHP module curl enabled. Check your php.ini

@JeromeBakker

Thank you very much for your help!
This tutorial helped me a lot:
https://www.geeksforgeeks.org/how-to-enable-curl-in-php/

Cheers

Christoph