You can add your client PO number to any job by heading to the settings tab on a job and entering it which will in turn pull through to any existing or newly created draft quotes and invoices on that job.
If you wish to add multiple POs, we recommend using a "/" between the different PO numbers. Alternatively, you can use the Reference field and rename it to PO Number - useful if you have multiple POs but want to share different ones on different invoices.
Note: Xero only has a reference field so the PO will be recorded in this reference field on Xero. If you are also using Streamtime's Reference field, both will pull through to Xero's reference field.