When you send a command that has Command Data and the command is expecting Result Data as well, and the communication is made using T=0 protocol, then you need to send two APDUs. One for the command itself, and another one to retrieve the result.
61XX
is not an error. It is a (successful) Status Word that indicates you have XX
bytes of response which you can retrieve using GET RESPONSE
(INS=0xC0
).
Here is the reference of the command.