FPY1 and ACH file generation

We are in need to execute FPY1 and generate the outgoing file in ACH format.

The FPY1 is successful but I am running SAPFKPY3 to generate the file, it errors out saying "No payment medium created".

Our requirement is to generate plain ACH file. No smartform or sap script etc.

Any pointers on what am I missing?

Thanks