The record button is greyed out because the Ninja V is not receiving a signal. Open the Ninja V operating menu by touching on of the display windows at the top (e.g., Time Code). See if you are getting an input. You can also see the resolution and frame rate at the top of the viewing window. Make sure the HDMI cable is connected to the HDMI IN port. Make sure the source is set to HDMI (not SDI) In the AX700, if you are shooting 4K, you must select whether the video will be displayed on the LCD or via HDMI. You can't do both. 1080p output is automatic and can do both at once. Try a different HDMI cable.