From the web page of TopCashback.com:
GET $30 BONUSES ON TOP OF YOUR CASH BACK
Refer friends and you'll each get $30.
Bonuses are unlimited!
For the Refer a Friend bonus to be applied to your account, your friend must authenticate their TopCashback account and reach a minimum cashback threshold of $10 cashback.
The Cash Back must be pending in your friend’s account within 180 days from the time and date they joined TopCashback.com.
Your bonus will become Payable when your friend has a minimum of $10 cashback at Payable status.
It's time to get your Invitation.codes account too 😎