Hello.
i`m testing with hdmi out camera and Herelink.
HDMI fpv camera is this product. (URL)
and when connect FPV camera and monitor, video is screen on monitor.
not screen with Herelink.
i heard about some camera is not suitable with Herelink.
but i need this HDMI out FPV camera.
so can you help me for using This FPV camera ?
can i screen video adjust some parameter ?
It simply looks not compatible
You can try to connect camera so that when powering your craft and herelink, keep camera hdmi cable connected to air unit hdmi IN1, when everything else is powered up and the boot sequence is done, connect power to your camera, could be that herelink will then regonaise your hdmi signal from the camera. Works for me with another brand cheap pilot (action) cam, takes a moment to picture to show up but its solid after that. Good luck and dont fry your equipement, this method worked for me, cant guarantee what it does in your set up. 
I am using the Foxeer Box 2 with HDMI. it was working fine, but the battery kept dying on the Box 2(it only stayed on for 12-15 min), so I went into the app for the Box 2 and changed the resolution down to 1080P 60Hrz. and that worked good for a while on the bench testing and the camera stayed on for an hour. But now the video feed does not show up on the screen at all.
Is there a setting in the Herelink that needs to be adjusted, or is it something in the camera?
What is the cheap CAM that you used to connect to the Herelink telemtery system
I know this post might be a little old, just want to share the solution that works for me. I am able to get the Hawkeye Firefly Split 4k to work with Herelink by updating the camera to older firmware.
Follow this link to download the firmware: Hawkeye Firefly 4K Split Cam Firmware 鹰眼 4K 卡录 固件 0906 - Split Cam - Hawkeye 鹰眼弘创科技 - Powered by Caogen8.Co!
The issue seems to be for newer firmware, the HDMI output is set to 720P 60FPS, which will not work with Herelink video link.