Allows for ingestion of payroll related data via Paystream. This includes: Employers, Workers, Pay, Time Worked, Time Off, Benefits, and Deductions. By default, items are processed asynchronously. Pass synchronous=true to process items inline. On synchronous responses each item carries an additional processed field with the Salsa IDs of the entities created/updated (matching the dedicated /paystream/{employers,workers,payroll-elements,risk-insight-inputs} endpoint shapes). On asynchronous responses processed is always null. Request size limits apply (items per request, and workers, employers and payroll element entries summed across the request); an oversized request may be rejected with HTTP 400 and a message naming the limit and the observed count.