Samsung - Galaxy S9+ - star2lte - Documentation Suggestions

Hello, for my SM-G965N I followed the tutorial up to ‘adb sideload e-0.16-o-20210422111918-stable-star2lte.zip’ but I get

E: failed to verify whole-file signature
E: Signature verification failed
E: error: 21

What are the likely causes ? Did I skip a step ? Am I missing something obvious ? Something about OEM unlock timing ?

In case this helps with understanding the context, the recovery boot tool header says:

Android Recovery
samsung/star2lteks/star2lteks
10/QP1A.190711.020/G965NKSU3TFK1
user/release-keys

I bought this precise model because I read that the “Easy Installer” supports it… I’m disappointed it doesn’t. “Your SM_965N is not yet supported by /e/ OS”