(Write here your question/remark)Please help us help you and fill where relevant:
Your LimeSurvey version: 6.13.2
Own server or LimeSurvey hosting: docker container
Survey theme/template:
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Hi,
I am working on an integration between my Java web application and LimeSurvey.
I have a database of users that I would like to ask to participate in one or more surveys defined in LimeSurvey.
The add_participants() function adds the participants but does not check for duplicates and in any case I have no way of knowing whether a particular user has completed all the surveys to which they have been invited.
The central participants function seems more usable to me, it checks for duplicates and maintains a unique repository of users, but it doesn't seem possible to invite a user to a questionnaire via rpc (only via the GUI?).
Nor does it seem possible to get a list of all central participants.Any suggestions? 

Thanks in advance.

Emanuele