Agree the decision criteria before the campaign launches.
Those could include cost per qualified lead, cost per acquisition, revenue generated, ROAS, conversion rate, lead quality or another commercial KPI appropriate to your business.
You can also use secondary metrics such as CPC, CTR and landing-page engagement to understand what is happening, but they should not become the definition of success.
At the end of the test there should be a clear decision:
Scale it. Keep testing it. Or stop spending.
That is far more useful than running ChatGPT Ads indefinitely because it feels like a channel your business ought to be using.