There's a problem when importing via CSV and then Setting postage for multiple items.
Occasionally when you have set post and you go to pay for it, it reverts to a failed state - The money has been taken by paypal, Yet the postage label cannot be printed because it is in a failed state..
Due to its state, you cannot also cancel or ask for a refund on the item as all options greyed out.

If you click regenerate labels Then you get these messages.
"At least one of the orders in your selection is in an invalid status.Error reference: 427b27f9"
"Request failed with status code 500"

A workaround for this in the past has been to go into each individual postage item and click regenerate postage label from the address screen. This no longer works.