I cant see to tell see where I tell them I'm expecting a parcel. Is that the add new delivery box ?
When your logged in on the my account page there is a button called 'Add new delivery' click this and fill in the form.
According to there instructions, you do this first or do this not matter ?
It doesn't matter, from what they said you don't even have to pre-inform them of the delivery it just speeds up there process.
I did the 'add delivery' on their website first then purchased in IComp.
Let me know how you get on, or if you have any other questions