To start, you could use Postman to try the API.
Currently the endpoint is : https://canssens-seo-extraction-v1.p.rapidapi.com/seo/api/
You have to setup some headers in order to realize the request.
Just add one parameter url as x-www-form-urlencoded
Example :
If you received a code 200, everything is OK.
You should get the analysis of the major Html anchor of the webpage.