Open supports single company as of now. This means you can sync your Open account with a single Tally company.
Using the plugin, once you login with your Open account on one of your companies in Tally, these two get auto-linked. Hence, if you trying logging in with the same Open account on another Tally company, you'll get following error message:
If you wish to sync multiple Tally companies on Open, we suggest you to apply for separate Open accounts for each company.