Most eCommerce brands focus on getting the “Add to Cart” click. But what happens right after is often a missed opportunity.

A fast-growing D2C health supplement brand recognized this blind spot. They noticed that customers were adding one core product—say, a multivitamin—but skipping complementary items like protein boosters or immunity blends, despite their relevance.

Rather than relying on static recommendations, they used CustomFit.ai’s JS execution feature to trigger an interactive upsell pop-up the moment a user clicked “Add to Cart.”

The pop-up offered a smart suggestion:

“Boost your results—add this supplement at 25% off!”

This real-time interaction showcased a complementary product (based on what was added), along with a clear incentive. The experience was smooth, targeted, and triggered only on relevant clicks—thanks to on-click JS snippet execution and upsell widget logic built directly within CustomFit.ai.

To refine it further, the brand ran A/B tests comparing different upsell items, discounts, and messaging. They experimented with:

• Bundles vs single product suggestions
• Flat discounts vs time-limited offers
• Different product pairings based on cart content

The result? A 2x increase in upsell success rate within just a few weeks—along with a steady rise in average order value (AOV). Customers appreciated the relevance and the deal, and the brand captured revenue that previously slipped through the cracks.

With CustomFit.ai, marketers can create high-impact, real-time cart experiences that respond to user actions, not just static rules—no dev sprint or heavy integrations needed.