Synchronous receiver

How to find out which data type returns FTP Syncronous receiver? How to set up XI to store synch messages?

I use BPM and sych step. ID with content based routing and 2 synch recever (JBBC, FTP)

I have got an error when bpm sends data. But I cannot find an error beacause XI doesn't store message content. I have generic Response data type and interface in BPM that works fine with JDBC Synch receiver but doesn't work with FTP Synch receiver.