Company tells the worker a delivery pays $15, you tip $5, the company reduces their portion to $10, the worker gets $15 total. You tip $10? The company pays $5, worker still walks away with $15.
- We will pay you $X
- We will make sure you make at least $Y
If you make the wording changes
- $X == <wait staff minimum wage>
- $Y == <normal minimum wage>
Then it becomes clear that this is exactly how restaurants work; with the caveat that it's per delivery instead of per hour.