I have this local.settings.json in my local Azure function (Timer trigger)

{
  "IsEncrypted": false,
  "Values": {
    "AzureWebJobsStorage": "",
    "FUNCTIONS_WORKER_RUNTIME": "python",
    .
    .
    .
  },
  "ConnectionStrings": {
    "sql_server": "valid connection string"
  }
}

I managed to access the connection string locally using:
conn = os.environ["ConnectionStrings:sql_server"]
and my code runs okay.

But, when I deploy I get ‘Failure Exception: KeyError: ‘sql_server’ […] getitem raise KeyError(key) from None’.

I tried to execute in portal changing that line to:
conn = os.environ["sql_server"]
But nothing changed.

Does anyone know how I can call this method on Azure Web?