Linux (Ubuntu) malformed entry file during install prevents update


During install (following the directions at: https://brave-browser.readthedocs.io/en/latest/installing-brave.html#linux) I get a malformed entry error when trying to update just prior to installation of the Brave browser. Terminal text of the entry error:

user@Linux:~$ echo "deb [arch=amd64] https://brave-browser-apt-release.s3.brave.com/$UBUNTU_CODENAME main" | sudo tee /etc/apt/sources.list.d/brave-browser-release-${UBUNTU_CODENAME}.list
deb [arch=amd64] https://brave-browser-apt-release.s3.brave.com/ main
user@Linux:~$ sudo apt update
E: Malformed entry 1 in list file /etc/apt/sources.list.d/brave-browser-release-.list (Component)
E: The list of sources could not be read.

My Linux build refuses to update until I (root) delete the offending entry (at which point it updates as normal).
Assuming the $UBUNTU_CODENAME command was malfunctioning, I replaced those instances with the codename of the build I’m currently running, with identical results.

What am I missing?