Broker API access for old trading account?

I opened my alpaca account long time ago before the broker API was introduced. In this new world I can only access Trading API, but not Broker API (which returns “message”: “forbidden” for all Broker API calls with the key and secret of my alpaca trading account).

I want to get NonTradeActivities like DIV (dividend) in the account via API, which is under Broker APIs. How can I access it? Is there a way to convert trading account to broker account?

Thanks for the help!