521 Error on a Client's Website

Hey everyone, I'm having a real struggle with the website of a client. I have reached out to GoDaddy and tried every single troubleshooting step I could think of with no luck. I was hoping that maybe one of you has a solution in mind for this kind of error? I'm not sure if this is the right place to reach out to but this issue is really a problem and it came out of nowhere seemingly as everything was operating perfectly yesterday morning. If anyone here can help, id really appreciate it!