Each user will be create one by one by calling the CREATE method. But each night, I need to update data of all users and send the changes to ACS.
Do I need to call 2000 times the PATCH method for each user or is there a way to pass a list of users data to update with an unique request ?
Can we use the method CREATE in order to update the data of an user if he is already known by ACS (from is email, id ?) or have I to send a GET request to know if my users already exist in ACS and after that make a CREATE or a PATCH ?
PATCH method is not used for the bulk update. You should always use the File Loading methodology inside a workflow for bulk processing and apply a signal to start the workflow whenever you want, Adobe Campaign Standard API
APIs should be used for small transactions. If you wish to use this, then you have to call the API 2k times.