How to interact with third party databases?

Question

CMS

Hello!
I don’t even know how to correctly describe what I need, forgive me for my lack of competence in this matter.
It is required to set up a cash-back service on the site (modx). There is a partner office, on one resource, I need users who follow my link to receive a reward from me. The whole process should be fully automated. Which specialist should I contact to solve this problem and how is it all correctly called on those. language?