Revenue is not the test
Advertising judged on revenue alone almost always looks successful, because revenue ignores what the goods cost. The test is whether gross profit on the attributed revenue exceeds the spend.
The break-even return on ad spend follows from your margin: at a 30% margin you need 3.33 shillings of revenue per shilling spent just to stand still. At a 20% margin you need 5. Most campaigns that get repeated have never been measured against that line.