Create System Users. If this is the first time you create a system user, you do not yet have a admin system user token. Start by getting yourself a real admin user’s access token in Business Manager.. Use your admin system user token or your own admin user’s access token to create a system user.. Here are the requests you need to get a system user token and make API calls.

https://developers.facebook.com/docs/marketing-api/businessmanager/systemuser