I noticed 3900 is not an option when adding SBCs. Can you check when this will be available and what option I should pick for the time being? I noticed version 3820 but not sure if that is the best option.
Unfortunately ACME 3900 is currently not supported in the current version 11.5. For full set of supported UC products in 11.5 Help:
Deployment and Installation > Deployment > Deployment - Unified Communications > Supported Products
And here in Community:
IR Community > Learning > How to Guides > Prognosis for Unified Communications Supported Platforms