These are the steps:
1) Launch Watson app. Make sure login to your account. Put all required items in basket.
2) Launch ShopBack. Goto "Watsons" menu.
3) ShopBack will use its own browser to goto Watson Online. Ensure to login to your Watson account in this ShopBack browser.
4) Check your items in basket. Hit "Checkout" button.
5) Scroll to the bottom for e-Wallet payment option. Choose GrabPay. Careful, there is also Boost e-Wallet option. Don't be greedy... LOL...
6) ShopBack will connect to GrabPay service. A 6-digit MSOS code will be delivered to link with GrabPay account. Pray hard your telco doesn't spoil this process. Else, use HSDPA / 3G connection if you're out and about.
7) Check the amount to pay and pay with GrabPay wallet.
8) Keep smiling or give your cat a bath. By then, 4.5% cashback (from ShopBack) and 20% rebate (from GrabPay) will be yours.
9) Meet me and give me 50% of total rebate... LOL...
memang masta nie..