Have you installed the AFL package and created the AFL Wrapper procedure in your environment?
Also, make sure you have the AFL__SYS_AFLPAL_EXECUTE and AFL__SYS_AFL_AFLBFL_EXECUTE roles in your user; they need to be granted by the SYSTEM user.
I haven't used AFM yet, but I'd also refer to the item 6.6 Developing Procedures Using Application Functions in the HANA Developer Guide.
Best,
Henrique.