signed embedding url for a dashboard

[Gabriel_Corail]

I tried to generate a signed embedding url for a Looker explore from the UI, and everything went well

Now, I'm trying to generate a signed embedding url for a Looker dashboard using the UI

When I go to the generated url, I get the error: 

That page doesn't exist or you don't have permission to view it.
If the URL is correct, check with your admin to make sure you have the correct permissions.

When I test the generated url with the Embed URI Validator, it tells me that the signed url is good (but it's not)

Any idea what's happening?