Varnish purge is not working in SiteAccess Host Matching on eZ Platform Cloud.
is not empty and contains the "Secured" SiteAccess (admin) host.
Then when you call the purge you've got:
We fixed the issue by adding this block in our security.yaml
We are not saying that is the best way to fix it, but that is at least enough information for you to do it
Thanks, @Florian Alexandre to help to tackle this one.