I did the same thing, seems that the Post Office cannot accept prepaid Parcelforce parcels, they can however accept it when it is being paid for at the time and send them through Parcelforce…
Thats what the wee nippy sweety at my local P O told me anyway. I’m not certain if I believe her not though, she’s a wee hitler.
they’re generally OK about pre-paid parcelforce postage at my local PO. I tend to print postage at home just in case I can avail myself of any cashback discounts before clicking through to parcelforce. It was the fact that the box was too big to fit through their hatch that elicited the “computer says no” response.
Felt like saying, well, do you climb through the hatch to get to work every morning, or is there a door somewhere that you can open?