That may be the TLS issue. Unfortunately you are using the ASP version of the extension that we stopped supporting a decade ago. I don't remember how to test the TLS version or change it in ASP, so I'd have to do some digging to figure it out. Have you talked to your hosting provider to confirm the TLS version has been updated on your server?
Send the new error to UPS support and see if they can shed some light on it. The "/Rate" endpoint is the correct one, so you don't need to test with the others.