I Downloaded Rhino Trial but SW demands a serial or quits?

I thought I was downloading the trial version of Rhino but I am getting asked for a password when I open the app. The options are buy a license, enter serial or quit. What am I doing wrong? Thanks

The Mac version of Rhino requires a license key and it was sent to you in an email message when you requested it. It starts with MR50-XXXX…

To save the license key on your system, you will be asked for your local Admin password just as you would be for many of the tools in the System options.

I looked up your email address and I found the Mac eval license key, but no record of any email messages being sent to your address.

How did you manage to get the DMG file downloaded without sending a request?

If you can’t find your key, go back to this URL and request it again.
A message will be sent to your email address within a few seconds of requesting it.