You can use various APIs in a client program to invoke Enterprise Server for .NET CICS programs using EXCI (External CICS Interface).
All of the APIs make use of parameter values and return codes that are specified by the IBM EXCI interface. See the IBM CICS documentation for more details.
Micro Focus supplies the copybooks DFHXCPLO.CPY and DFHXCURM.CPY for use with COBOL programs that use EXCI. The MicroFocus.SEE.Comms.Public namespace, in the assembly of the same name, contains enumerations ExciResponse and ExciReason for EXCI response and reason (error) codes.