[N00b] PoE Injector for business IP cameras, do I really have to provide 1 data input for each data output?

Hi friends and thanks in advance for being awesome.

I bought this PoE injector, apparently thinking it was a PoE network switch:

WS-GPOE-16-48v240w Gigabit Passive PoE 16 Port Power Over Ethernet Injector for PoE Cameras, IP Phones, WiFi Access Points, Includes 48 Volt Power Supply 240 watts https://www.amazon.com/dp/B01H990ADQ/ref=cm_sw_r_cp_api_i_-p.jDbDW179C3

I’m trying to install/connect 8 IP cameras, a security alarm, router and 4 IP phones. I didn’t realize this until now, but it appears for every Power+Data connection OUT, the injector requires a data input.

My problem(s): 1. Holy spaghetti 2. How in the heck can I supply 16 data inputs off of the only 4 original modem outputs I have to work with?

All the blogs I’ve read/videos I’ve watched start with the assumption that I know how networking works, and maybe I’d be better posting this in r/ELI5?

Does anyone recommend a cleaner solution?

Thanks again!