Hi Matt,
If it is this camera https://amcrest.com/amcrest-3mp-bullet-wifi-video-security-ip-camera-pt-ip3m-943w.html with no PTZ
Armcrest have a relative standardized way to connect to their cameras so test this one. In Custom URL use rtsp_tcp and the address:
rtsp://username:password@IP:554/cam/realmonitor?channel=0&subtype=1
channel 0 is the main channel. It can also be 1 for the extra stream.
Please report back if it works.
-Henrik