Hello all!
Nice item being shown here. I agree that this is an 1861 use. I was part of the discussion on the U.S. board.
I am more familiar with the paid markings on outgoing mail from the US which would show the money passed on to the next postal service rather than the full rate as this one shows. However, I can say it was fairly common to note the full amount paid in US cents in the exchange marking.
I will look in my records to see if I can find others similar to this marking. I do not know if anyone has determined for certain if these devices had a slug to insert different rates or if the rate was welded into place. However, the existence of those without an amount and only the word "Paid" might imply a rate slug could be put into place.
I am more of a rates and routes person, so I'll ask a couple of people who like markings if they can help.
Rob