The VP3600 is an SRED device. SRED devices require a DEK (data encryption key) to function. Without a DEK injected into the reader, it will only display need client key. Typicly Typically the DEK is specified and injected at the time of purchase by ID TECH or a distributor. Contact the provider to learn of you your options to key get your unit key injected.
SRED Information from PCI Security Standards Council