Hi Eric,
As for the file format, you need to go to OBPM1 (Payment medium format) detail screen for the PMW/DME you are configuring and need to select Payment medium without doc > Type = 1 File, then SAPFPAYM program should create those formats.
Now the directoru to store the payment file needs to be specified in the field "File Name" in the selection parameter of SAPFPAYM (FBPM) withyour PMW and also need to ensure that you select "output to file system" as well.
Would you like to try these above and let me know how it goes?
Kind regards
Taro