Relate tickets to one another via REST API


I need to create a relationship beetwen change and request (RequestedCausedByChange type). With documentation and this topic  I was able to create a body for my post:

where XXX is the Id of my request and YYY is the id of my change. I use EMS/Bulk API. I got error 500 though I do not see any reason why?

Do you have any ideas what to change in my body to get the relationship done?
Marcin Plisz