It is not possible to create a purchase order from an invoice. However, you can create a purchase order manually in QuickBooks Online by following these steps.
Also, you can check on this article for your reference: Copy a quote to a purchase order.
Let us know if you need further assistance. Have a nice day!
You can create a quote on another app and integrate it with your QBO. Once your client approved it, you can convert the data to purchase order with a single click.
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