In general, you don’t need multiple licenses; your subscription allows you to use Mercury with all production data platforms in your enterprise.
However, there are circumstances that might require multiple licenses/subscription; these typically involve unusual security requirements or otherwise segregated data access.
For example, if you are using Mercury with Microsoft Dynamics 365 Business Central in the cloud, that architecture limits us to a single server (as many companies as you wish, but one server). If you add a new server (with its own D365 BC URL), you must obtain additional subscription licenses, even if the same user will be accessing both servers.
If you’re unsure about your circumstances, please contact us at support@mercurybi.com.