It says "you can pay by cheque, postal order, cash etc at any Post Office..."
So the Post Office act as a currency exchange in this instance exchanging cash into money of account and discharging the account...
I'd rather use the cheque they started for me though... :D
Printed copy · Anthology Volume 7, page 812Printed copy from The Tender For Law Anthology, Volume 7, page 812 (printed 13 June 2014). Added by this site; not part of the Facebook export.