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Once an item has been added to your basket it will be greyed out (unless you have the client option activated to prevent this)
Can I create a standing order?
There is no standing order functionality but there is a client option to let you copy an order an order you have previously sent.
If the client option is activated for you you can click on the PO number from this page and you will see a Copy Order button underneath the order. Click on this and then you can edit the quantities and add more items in the basket.