For the support of European payload operations on board the International Space Station (ISS) ESA has applied a distributed operation concept with multiple User Support and Operations Centres (USOCs) located across Europe. Each USOC supports a variety of tasks related to the preparation and in-flight operations of the European payloads assigned to it. To ensure the necessary qualification and certification of the USOC operators, generic coursed as part of the ESA training concept is provided by the ESA European Astronaut Centre (EAC), supported by the Columbus Control Centre (Col-CC) and the Industrial operations Team (IOT). Complementary to this, each USOC is responsible for its own payload specific training. This paper focuses on how the Belgian B.USOC and the Erasmus USOC supported by the Netherlands and Belgium, used their experiences of nearly two years of continuous ISS payload operations to develop and implement a dedicated payload training concept for their operator. It outlines the approach for continuous improvement of the USOCs' specific training and explains the training concept used for current and future payloads. Complementing the generic course, the overall USOC operator traiing covers internal and external theoretical courses, as well as practical exercises consisting of On-the-Job training (OJT), Stan-Alone Simulations (SAS), European Simulations (ES), and Multi-Segment trainings (JMST).