Unfortunately, Purchase Plus does not allow that function. There are however three ways to work around this if the documents are already processed, and they are to be kept.
1. Put a note on both the Invoice and the Purchase Order in the 'Comment' section, noting that they belong to one another. We recommend checking with your Finance team to ensure they approve of this approach.
2. If the Invoice is to be kept, [Cancel] the Purchase Order.
Create a new Purchase Requisition from the Invoice, but ensure to [deselect] the [Send to Supplier] box and write a comment such as 'Do not fill this order' in the comment section.
3. If the Purchase Order is to be kept, contact Purchase Plus support and request that the Invoice is reassigned to the relevant Supplier.