Only Echos with a screen (Echo Show) can take this call; Echo Dots refuse it.
Your phone or laptop camera and microphone are sent to the chosen Echo through the hub. Say or tap "end" on the Echo, or press Hang up here, to finish. Use https (the Tailscale address) so the browser allows the camera.
Sound from the Echo:
On an Echo Show, tap or hold the microphone / talk button on its screen to talk back to you; until then it may stay silent.
Ready.