I wanted to ask two questions.

1

I have two questions: first, is your certificate valid here in Brazil? And second, do you teach this subject—specifically basic knowledge of web development (building REST APIs)—and how can I sign up to study it?

2

The certificate just means you completed the course. It’s not very relevant to getting you a job but it’s for your own personal gain.

3

Welcome to the forum @roberto100,

There is some coverage of REST APIs in this curriculum:
Back-End Development and APIs Certification | freeCodeCamp.org

Happy coding