Policy extension source

I'm trying to add an extension from a custom repository on azure blob but the error below pops up every time.

I've also try to force the origin (also any origin) as trusted source.
I also tried to add the extension id to the allowlist

To be honest it seems that the policy "extensioninstallsources" is ignored also if it's correctly loaded (see status).

We have a strong need to distribute the extension internally without publishing it in the store.