This error happens in most cases due to the servers going through problems or being under maintenance. Besides that, it could also happen when your Roblox game client is outdated. Here is a list of all the methods that you need to do to fix the following error:

1. Check for a server issue

Most of the time, a server issue or scheduled maintenance is the leading cause of the Roblox error code 400. You first need to check the server’s status to see if the servers are down. Most likely, the central server for finding matches is down, and developers are working on it to fix it. You can use sites like Downdetector to check the server status and see if other people have reported problems with the server. This site will show how many reports have been made in the last 24 hours. This will let you know if the error code 400 in Roblox is happening to others or just to you. You can also go to the Roblox Twitter page to see if the developers have said anything about servers being down. This page is dedicated to updating users about the current server status. If you found recent posts about server problems happening, read the comments to find out what other players have said about it. If you can confirm that there is a problem with the server and other people are also experiencing the 400 error code, you can only wait until the developers fix it.

2. Perform a Winsock Reset

Roblox error code 400 might be caused by network inconsistencies. A Winsock reset should be enough to fix these issues since it will clear temporary network data.  A Winsock reset is a command that will also reset some important settings to the ‘safe’ defaults, which may fix the problem in your case. All you have to do is to use the Command Prompt with administrator privileges. Note: This command won’t affect your computer files or your access to the internet. Here are the steps you need to follow: If the error code 400 still appears even after doing this, try the next fix down below. 

3. Run Windows Diagnostics Troubleshooter

Another thing you can try is to run the Windows Network Troubleshooter. This process will scan your network to see if it finds any problems. If problems are found, the troubleshooter will attempt to fix the network issues automatically. To run the Windows Diagnostics Troubleshooter, you must go to the Windows Settings and find the Other Troubleshooters. The Network Adapter should be there – run it to start the troubleshooter. Here’s how you can do it: If you’ve tried everything and the error still appears when playing Roblox, go to the next and last method available.

4. Change DNS to CloudFlare or Google

The last thing you should try is to change the DNS to Cloudflare equivalents. This should fix your problem because you are moving your DNS range to a more stable domain name address. This can be done from the Control Panel window of your computer. This fix can be replicated on every recent Windows version.  Here is a guide that will show you how to do this:

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