If you are trying it on SMP 3.0 SP04 PL01 (latest release), there is one option in gateway (GW) cockpit to test the destination before running service document.
e.g. In GW cockpit, there is a default service available "ESPMService", to run this service, you have to create a destination which is of type JPA.
Can you once confirm if you are running the service document URL only. e.g. https://localhost:8084/gateway/odata/sap/EspmService;v=1
That note is pointing to this link Managing SAP Mobile Platform Server Features - Administrator - SAP Library but it doesn't talk about JPA. I doubt if you have to deploy any jar file to SMP pickup folder. I haven't read it anywhere.
Let us call Bjoern Woppmann to clarify on this.
Regards,
JK