Try another computer. Maybe your computer has a security firewall or something, so it is forbidden to ask the website.

Another possibility is that you didn't install the required software on the website.

The third possibility is that the website server has just been closed for maintenance these days and can't be opened.

The fourth possibility is that there are many visitors in the last few days, and many people hang up to study, so the website can't be opened.

I've hung up with many colleagues and occasionally met them. I won't hang up on the same day when it's important. It will be normal in a day or two.