I'm sure this deal was on shortly after launch too so would be interested to hear how people got on.
Firstly you have to be approved for the credit account and purchase the iPhone using that credit account.
The offer is 10% credit back to your credit account after 30 days.
This should happen automatically without claiming.
The Buy Now Pay Later can be over 6, 9 or 12 months interest free. Doesn't specify that it's for new customers either so seems open to all.
Not sure if there's a delivery charge and they are proposing delivery by 14th November.