Hi Hady,
Firstly, could you edit your post and include a reproducible example of what you've got so far and the errors you have?
In terms of advice for working with APIs? I personally like the R package httr.
- An Introduction to Web APIs
- Here's a vignette on Getting started with httr
- Here's a vingette on getting started: Best practices for API packages
And I personally like purrr for wrangling xml and json objects. Here's a tutorial from Jenny Bryan on the topic, How to tame XML with nested data frames and purrr