On the camera side the specs can get a bit confused sometimes. For instance I bought some Reolinks I thought were POE from the listing but it seems the WiFi models do not support POE while the exact same models without WiFi do. You need to sort out which POE type it wants. Generally this going to be 802.3af or 802.3at but Unifi for instance has some stuff that only support 24 volt passive. And some others have they own ways of doing things so read carefully. And of course if the camera does not support POE directly but is powered by 12 volts you can always use the Huacam HCP05 Passive PoE Injector/Splitter with 5.5 x 2.1 mm Connectors. With good cables I've managed up to 200 feet with them.
You need to make sure the POE injector and the camera are the same type. The PoE Detector for IEEE 802.3 or Passive PoE - Quickly identify Power over Ethernet; Display Indicates Passive or 802.3af/at; 24v, 48v, or 56v; and Mode B Reverse Polarity is a nice cheap tester to see what is coming out of your switch. Note it sees 12 volt passive as 24 volt. Though I'm thinking something a bit more might be a good idea.
For instance I found this switch on sale. The PoE Detector for IEEE 802.3 or Passive PoE - Quickly identify Power over Ethernet; Display Indicates Passive or 802.3af/at; 24v, 48v, or 56v; and Mode B Reverse Polarity shows it is putting out 802.3at while my trusty WS-PoE-Tester - Inline Tester For Power Over Ethernet | Display 20 to 56 Volts, 0-5 Amps And Display Actively Used Power 802.3af/at and Passive PoE at 10/100/1000 Data Rates says it is outputting nothing without a matching POE camera on the other end. They have a newer version called Inline Power over Ethernet Voltage and Current Tester (PoE-Tester-Gen2) which does both. Though I'm also looking at the Triplett / Byte Brothers POE1000IL Inline POE Analyzer which seems to do a bit more.