theres is a postage section down the bottom, (right hand side I think)
insert the correct amount in there
BUT do not press RECALCULATE - the button's name is a little misleading and should probably say aefresh or start again or restore etc
Instead, press "preview" and once you check things, send, or just hit send straight away.
I reckon you are getting caught out with the recalculate button.
Some people can go their whole lives and never really live for a single minute.
