hi Freya. Here are a couple suggestions.
1. Your tabcmd version should match to your Tableau Server version that you're trying to connect to. You can "tabcmd version" to see what version you have installed, and then verify it matches.
2. Your error message mentions something about certificates. If your Tableau Server is SSL enabled, then when you login using tabcmd you may have to add a tag of --no-certcheck https://kb.tableau.com/articles/issue/error-certificate-verify-failed-when-using-during-tabcmd-login
The server you are running tabcmd from doesn't have proper root certificate it seems.
--no-certcheckoption to each command being run. It will ignore the certificate check.