Signed URLs working, but not when "Require Signed URLs" is turned on

Hi All,
We have implemented signed URLs for our Cloudflare stream videos using the python client tool:

They work great, but only if “Require Signed URLs” is turned off for that video.
As soon as we turn on “Require Signed URLs”, we see the message “You don’t have permission to view this video”.

Is there a bug here or might we have missed something?
Many thanks!