I'm trying to assign DSS/BLF to a Function key on a DTU 16D

I press Feature key, press Redial
Press the function key I want to assign and Get ERROR

What am I missing ?

Feature Access Keys have to be programmed on the buttons in order to use them as a "one-touch" speed dial.

Memory Block 4-12 is used to add Feature Access Keys 01 - 10 on any key. LK 6 is used to select the FA option.

Thanks , that looks like it should do it