Home Assistant provides a RESTful API on the same port as the web frontend (default port is port 8123).
If you are not using the frontend in your setup then you need to add the api integration to your configuration.yaml file.
http://IP_ADDRESS:8123/ is an interface to control Home Assistant.
You can obtain a token ("Long-Lived Access Token") by logging into the frontend using a web browser, and going to your profile https://IP_ADDRESS:8123/profile.