Download not available for SEP-SBE 12.1.6 upgrade

I currently have Symantec Endpoint Protection Small Business Edition 12.1.5337. I want to upgrade to version 12.1.6, so I can add protection for my Windows 10 users.

I am attempting to follow the instructions on this article: https://support.symantec.com/en_US/article.TECH230601.html

When I go to https://symantec.flexnetoperations.com and enter my serial number the only version that is available for me to download is version 12.1.5.

How do I get version 12.1.6??

Thanks in advance for your help!