Private add-on install fails; no request reaching backend, "Add-on is currently not responsive"

I’m building a private add-on for internal use in our own real Clockify workspace. The add-on shows up in the Marketplace as installable.

When I click Install, I get a loading spinner followed by two errors: “Add-on is
currently not responsive” and “Add-on under maintenance — We couldn’t reach Ripe Media
Invoicing add-on.”

I’ve verified the backend is actually reachable and returning correct content:

  • The manifest URL (https://clockify.ripemedia.com/manifest) returns a clean 200 with
    valid JSON when tested directly via browser and via curl, both through our normal
    domain and by hitting the origin server directly.
  • Our server’s own access logs confirm we HAVE received real install attempts from
    Clockify’s infrastructure before (Apache-HttpClient/Java requests, matching IPs seen
    in other forum threads about webhook sources).

Any guidance would be much appreciated. Happy to share more if useful.