Extend HA API

Hi everyone,
Is there a way to add my custom web api to home assistant?

I’m doing an integration project and from the caller I can call only one web method not a sequence of methods.
So I need that this method collects all required data in one json response.

considering that I can’t call this 2 methods in sequence:

I want to write a custom REST method that collects these 2 HA sensor state in one outcome.

Otherwise I’m interest to find out if there is a free service (webhooks?) that can do this.
I know that zapier can do this but not with free plan.