If you are trying to view the V3 cameras with Echo Show then try renaming the camera names in Alexa. I have several V3 cameras and they work fine with my Echo Show 5 (2019 1st gen) and Echo Show 8 (2019 1st gen & 2021 2nd gen).
If you are trying to enable Person Detection trigger with Alexa or Person Notification with Alexa, then I believe Cam Plus or Cam Plus Lite subscription is required.