Hi,
It took me a long time to figure out how to set the update TM field values due to a documentation bug. On this forum I found that this issue was reported 4 years ago (here) and the documentation issue is still not solved. Because of this, like Laurent, it took me a long time to debug this. Can someone at SDL please fix reported documentation errors like this?
Related API page: http://producthelp.sdl.com/SDK/ProjectAutomationApi/2017/html/7f54687d-2336-48f0-b70b-1fe051234be2.htm
Lennart