Here's my referral link for TopCashback www.topcashback.co.uk/ref/recklessladybird/?source=App-iOS-TAFPage
You do your online purchase as normal but first you go through the app/website and that's how you get cash back. A bit like you using the nectar website, but easier and faster and more rewarding.
I've used it for many years and never had problems. I do small purchases on eBay via the app and the money adds up. You can withdraw as a voucher (with extra bonus on top) or cash to you bank account.
If signing up via a referral link, we both will get extra payments in our accounts.