Account: 5+ years, sync daily, I have shared many decks successfully (sharing is enabled).
Tried: multiple browsers, VPN on/off, clear cache/cookies, reselect file, minimal description.
Package is a clean root-level .ankiaddon (no pycache, no wrapping folder).
Add-on / file:
AnkiWeb email is the same one I sync with in Anki.
Please check whether add-on upload is blocked separately from deck sharing on this account, or if this is a server/UI bug.