by Mathieu Petit-Clair.
Bonjour Timothée,
Moodle will generate documentation for all web services, under http://yourmoodle/admin/webservice/documentation.php
You might need to enable the ws documentation, under /admin/settings.php?section=webserviceprotocols
This should give you some information about all the parameters to use with core_cohort_add_cohort_members().