A few months ago, Turkish ISPs started blocking certain FiveM services which are used to download the client and whatnot. This has been problematic for players who live in Turkey or any other country where ISPs block FiveM for whatever reason.
Here’s a couple of solutions that will resolve your issue:
Antivirus/URL Filtering Software
Some of these issues are caused by these kind of software blocking FiveM from connecting to the server/website, to fix this you’d have to either disable this kind of software or add FiveM as exception
The best way to find out how to do this is to find out what software you are using and lookup the online manual and see how to disable it
Sometimes your network, ISP or country could be blocking requests to specific hosts, to fix this you can try using a VPN like hide.me couple of examples of this are Turkey and NET in Brasil.
Make sure the disk where FiveM is installed (default C:\) has enough disk space so it can download new patches and resources to cache.
The solutions above will resolve the issue for the majority of players experiencing them, however if the issue was not resolved, we recommend you create a topic in #technical-support filling the template in entirely and providing as much information as possible.