Hi
Sometimes in Germany they sell B-Ware at reduced price. These are new items already delivered to a customer
According to EU law you may - within 14 days - return the purchased merchandize without any need to provide a reason.
So the first owner may have done something.
If Lippe sold the unit as brand neu, there must be a warranty attached to it
Märklin's warranty is "24 months from the date the product was purchased from an official Märklin dealer, but no longer than 60 months from the time the item is removed from the catalog assortment."
Not sure for the USA but here, in Europe (EU), you send a message to Lippe and they send a sticker to be attached to the returned parcel so shipment is free of charge both ways.
Similar with Märklin: for an accepted warranty return, you pay for the shipment to them, they repair / exchange / ship free of charge and ask you to provide a shipment cost receipt so that you shipment costs are reimbursed (usually by CC.
Note: It is safe to phone first.
Two things are definitly abnormal are: serial number to be Zero and the stop bar not lighting (is it still turning the power OFF and ON?.
Note: I had a Märklin Insider loco for a bit more than 5 years that turned faulty but I returned to my shop in Paris and Märklin / Au Pullman managed to have it repaired free of charge.
PS: have you tried to connect your CS3 to a PC using a simple CAT5 CAT6 (Ethernet cable)?
How to?- go to your CS3 System: IP and fill an IP address like 192.168.0.23

-
- then on your PC, using your browser (I use Edge on Win 11) in the address field, type the IP address you have selected (e.g.: 192.168.0.23), alternately, using a "Box" / WiFi Router, will assign an IP Address and it will show on your CS3.
- Then you get a welcome screen from the CS3 giving you access to all fonctions (limited edition power on layouts, no simultaneous loco editing on both the PC and the CS3
NOTE: the screen on your PC may be different of the screen on your CS3 because you have two independent users (one on the CS3 doing some loco parametrization and the PC doing train control as an example)
Best of luck
Jean