Please help us help you and fill where relevant:
Your LimeSurvey version: 3.15.5+181115
Own server or LimeSurvey hosting: Own Server
Theme:
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We would like our customer system to be notified when a survey is completed, by making a call to https://ourserver/api/surveyCompleted?survey=&token=
I assume I would need to change the code, which is fine if somebody could point me to the code that handles survey completion. 
It would also be useful, but not as urgent, if someone could point me to the code that handles saving a partially completed survey. 

I confess I am finding the framework and architecture quite difficult to grasp. 

Many thanks in advance,
David

Please, do not double post.
You already asked this in "Can I do this with LimeSurvey?"

​​​​​​​Joffm

manual.limesurvey.org/AfterSurveyComplete

This looks *extremely* useful, many thanks.