I struggled a lot with this and turns out that for me, at least, the issue was with my VPN. I used NordVPN so it might be different for your case.
Just disconnecting the VPN was not enough for me. If you are using NordVPN you need to go to Threat Protection and turn off or pause Web Protection as shown in the screenshot below:
Once you do that you can regenerate a response and it should hopefully work.
Reason 2 might be that your browser is using a proxy. Try to turn it off. You will need to look for it depending on the browser that you are using.
The other reason might also be that openai is just overloaded at the moment! Let us know if this helped in the comments 🙂 Cheers!