I was using:
https://service.ringcentral.com/ringout.asp?cmd=call&username=17274003201&ext=7001 &password=XXXXXXX&to=17274106584 &from=17274106584&clid=7274003201&prompt=1
(I added space)
To initiate a phone call to my cell and then connect to a customer.
I know get this message:
<html>
<head><title>404 Not Found</title></head>
<body bgcolor="white">
<center><h1>404 Not Found</h1></center>
<hr><center>nginx</center>
</body>
</html>