The AFTP API calls do not return a value. Rather, the return_code parameter is set to indicate the success or failure of the call. You should check the return_code parameter after each call and handle error values appropriately.
The C keyword void is not used for entry points in the AFTP API. Instead, AFTP_ENTRY has been defined. AFTP_ENTRY is defined differently depending on the operating system on which the AFTP client is created.