Develop an API for a secure trade on the marketplace

We are going to launch a marketplace where some individuals will sell their belongings to other individuals. At this stage, we have received an agreement on cooperation from Tinkoff Bank (partner of the site as an acquirer). Now we need to develop an API that implements the possibility of a secure transaction on the site.
Silent information on the "safe deal": https://vc.ru/tinkoff/154635-bezopasnaya-sdelka-ot...