Hello ! 
Frist of all thank you for taking time to read my message.
Here is my problem: I would like to upload those retailer as user in my app with retailer 's manager’s emails but at my best tries i was able to create 700 users up to my 1000 users first request, then an error message occures.
Here is how i manage my request.
And it works perfecly when my list is about 100 entries. When I try with more than that it does not work so well.
This is how i initiate my Post Request:
I activate an API Workflow that structures a .CSV file to a plain text formated for the Post request.
then I use the previous API Call to create my users.
I also try with a plugin to manage my request and avoid server to get too busy but it does not works :
I also have tried to trigger data base event on list of Objects to simulate a bulk create thing but is does not work as well as I thought.
So I will be pleased if you have a brilliant idea to achieve my project.
Once again thank you for having take time to read my message,
Best,
Antoine