If you are using a UNIX server, set the A_DEBUG_USING_THIN environment variable to a non-zero numeric value before the transaction server initializes the runtime. This tells the runtime to initialize in a mode which allows it to communicate with the thin client. After you enable this mode, you may not use terminal or xterm debugging.
In Windows server environments, the transaction runtime is automatically initialized in the mode that allows it to communicate with the thin client whenever it is run from within a transaction server (such as CICS).