There are always two RJ-45 ports on a given PoE injector. One is Data-In
and second is Data-Out + Power
In case you need to connect two device while both are powered up by PoE injector, make sure there is an active network device between both data ports.
If you connect injectors directly, using Data-In
ports on both, there is high risk no data trafic won't be delivered.
This is caused by nature of voltage / current protection on Data-In
port which expects active device being connected.
Make sure you always use standard and tested UTP cable.