CICS® Transaction Server for z/OS®, Version 3 Release 1 does not support the Basic Telecommunication Access Method (BTAM).
For several CICS releases, BTAM terminals have been supported only indirectly: that is, by transaction routing from a back-level terminal-owning region (TOR) to which the terminals were attached. In CICS TS for z/OS, Version 3.1, this indirect support is removed. BTAM is no longer supported and all references to it have been removed.
This means that, if you have a network of BTAM terminals connected to a back-level CICS TOR, you will not be able (as you were in previous CICS releases) to route transactions from them to a CICS TS for z/OS, Version 3.1 application-owning region (AOR). You must either upgrade your terminals or route to a previous version of CICS.