Activate REST-API for health-checks

Hi all, I'm fairly new to the F5 and I need some help.

Some VIP's have configured health-checks to monitor if the Frontends are reachable (Iwas told).
Now I want to create a "Service" - basically a python script - that builds API-calls and send these via REST-API to the F5 Load-Balancer in order to get the status of the health-checks.

But so far I didn't had any luck accessing the REST-API. So I begin to wonder if it is acltive/enabled at all.
My curl requests return a 403 although user/pass is correct. I can access the GUI without a problem.

How can I check if the API has been enabled ?
And if it not running, how can it be enabled ?