Businesses can measure the success of a promotion or discount campaign by analyzing various key performance indicators (KPIs) such as sales revenue, customer acquisition and retention rates, website traffic, conversion rates, and return on investment (ROI). They can also track metrics like redemption rates, average order value, and customer feedback to assess the impact of the campaign on their bottom line. By collecting and analyzing these data points, businesses can gain valuable insights into the effectiveness of their promotional strategies and make informed decisions for future campaigns.