No, there's no limit.
For every group of 3 friends who each spend $200 with their Oobit card within 60 days of entering your code, you earn another $50 in USDT, or in USDC where USDT isn't available, such as in the EU.
Please share your code with people you know. Posting it on coupon or deal sites, self-referrals and using multiple accounts aren't allowed, and rewards earned that way can be withheld.