By default, Orders have all the items pre-approved, pending your approval of the order as a whole.
To reject any item within an Order:
Open the Order by clicking anywhere in the row with the Order number
Under each ordered item there is a colored button with a check mark and the text Approve. This means the item will be approved, if you approve the order as a whole. By clicking on this colored button, the box will turn gray and the check mark will be gone - this item will be rejected from the order.
Item will be approved
Item will not be approved
3. Approve the Order as a whole using the button marked 'Pending approval' at the top or lower right corner of the Order Details page. Select Approve from the drop-down menu.
Opening the tax invoice/order detail again, the items that were rejected will be listed at the bottom under the title Rejected Items.
If all items are unchecked and the Approve button is selected at the top/foot of the order, the order will be marked as REJECTED - this is because 0 items in the order have been assigned an APPROVED status.