Failed to notarize a "distribution" pkg

I'm building a custom macOS installer for my software, primarily using the builtin tools of codesign, pkgbuild, productbuild and xcrun.

My product consist of a list of plugins and a CEP extension for the Adobe After Effect app.

All of my bundles and binaries are properly signed using a trusted Apple Developer certificate I've generated, of type Developer ID Application.

My installer is a "distribution" pkg, and has this structure(expanding it using pkgutil --expand):

SceneTools-3.4.4-osx-installer
├── Distribution
├── miscellaneous.pkg
├── plugins.aftereffects2022.pkg
├── plugins.aftereffects2023.pkg
├── plugins.aftereffects2024.pkg
├── plugins.aftereffects2025.pkg
├── preinstall.pkg
├── Resources
├── scenebuilder.pkg
└── uninstaller.pkg

Each "child" pkg would install parts of my product in different locations in the target macOS disk(this is why I'm using that kind of style of building the custom installer).

Signing each and every bundle or binary of my product, signing the "child" pkg's, then notarizing them works well with no issues, in addition signing the "final" "distribution" using productbuild --sign option also works well, but when trying to notarize the "final" pkg, the notary service fails with this error:

{
  "logFormatVersion": 1,
  "jobId": "5fb38df9-ef97-4bd3-955e-7783c37ac4a8",
  "status": "Invalid",
  "statusSummary": "Archive contains critical validation errors",
  "statusCode": 4000,
  "archiveFilename": "SceneTools-3.4.4-osx-installer.pkg",
  "uploadDate": "2025-06-26T14:14:41.507Z",
  "sha256": "621de5d887b06ad11214255c6e91ebd9eeffb18ad8f940365f4539bd1902fe9a",
  "ticketContents": null,
  "issues": [
    {
      "severity": "error",
      "code": null,
      "path": "SceneTools-3.4.4-osx-installer.pkg",
      "message": "Package SceneTools-3.4.4-osx-installer.pkg has no signed executables or bundles. No tickets can be generated.",
      "docUrl": null,
      "architecture": null
    },
    {
      "severity": "warning",
      "code": null,
      "path": "SceneTools-3.4.4-osx-installer.pkg",
      "message": "The contents of the package at SceneTools-3.4.4-osx-installer.pkg could not be extracted.",
      "docUrl": null,
      "architecture": null
    }
  ]
}

My final pkg indeed doesn't contain any bundles or binaries directly, but that's how it should be - a container of "child" pkg.

I tried various ways of working-around this issue, like:

1. Notarizing the dmg that contains this final pkg - worked, but when opening the pkg, GateKeeper blocks the users from opening it.
2. Wrapping the pkg inside an .app and notarizing the .app - same as above.

What am I doing wrong? Does those kind of pkg like my "final" pkg aren't meant to be notarized? if so - how can I solve this GateKeeper blocks? Should I build my final pkg in a different way?