The cable connection is very simple.
If there are only the 315-2PN/DP and the Lumberg device, then in the Profibus connector on both ends:
Green wire goes to A1 and red wire goes to B1.
And in both connectors the termination should be set to "ON".
The only thing that must be set up in a Profibus slave is the station no. Usually it is done by dip switches. Have you done this and does it match the setup of the slave station no in the STEP7 project ?