Theme not applied

[githanium]

Hey all,

I might have not read the documentation properly and apologise in advance if this is the case.
I am trying to apply a theme at runtime when the server is started.
The login theme is loaded correctly and when I access the portal manually I can apply it and everything works as expected.
However I cannot do the same when loading the configuration from my realm.json file

Theme called modern

in realm.json I have

"loginTheme": "modern",

and within the client still in realm.json

"attributes": {
        "login_theme": "modern",
        ...
}

keycloak-themes.json

{
  "themes": [
    {
      "name": "modern",
      "types": ["login"]
    }
  ]
}

What am I missing? Why when I start the app the theme is not applied automatically and still need a manual input??