See https://tools.ietf.org/html/rfc4180, Common Format and MIME Type for Comma-Separated Values (CSV) Files.
The first line in the CSV file must contain the names as the column headers. Use the /CSV/headerNames API to get the list of header names.
Only one CSV import request can be running for the specified tenant.
If the default password is not specified, a random password will be generated and an email is sent with their password.
The maximum file size is 10MB.
When setting a value for the urn:ietf:params:scim:schemas:extension:ibm:2.0:User:linkedAccounts column, the value should be as follows: <externalId>@<realm>
When setting a value for the urn:ietf:params:scim:schemas:extension:enterprise:2.0:User:manager.value or urn:ietf:params:scim:schemas:extension:ibm:2.0:User:delegate columns, the value may be specified by name or ID. For example, testuser or 50GSYHD4C3.
Multiple-value attribute values are specified with a '|' delimiter which may be overridden with the optional multiValueDelimiter query parameter.
Attribute values that contain a special character (i.e. comma) must be enclosed in double quotes.
Entitlement required: manageUserGroups (Manage users and groups) or manageAllUserGroups (Synchronize users and groups) or manageUserStandardGroups (Manage users and standard groups), or manageUsers (Manage all users), or manageUsersInStandardGroups (Manage users in standard groups).
Note: You only need one entitlement, but you can have more than one.
post https://{tenanturl}/v2.0/CSV/importUsers