Since there is no public INAMI API but a web form available on the INAMI website.

I did a multi-process web scrapper on the website which is updating the data every month (without any impact on their website) and expose the data as an API (the datas are free to use).

The documentation is present !

The API is hosted on Heroku Free Tier and use MongoDB free mLab as storage.
The web scrapper is made using NodeJS and Puppeteer.