Heights turns its billing reminder into an upsell engine with a 760% lift

Heights is a supplement brand with a deeply loyal customer base built around its flagship Vitals line — the kind of subscriber base most brands would envy. That loyalty was never the problem. The problem was that the Klaviyo email program built on top of it — reliable, well-designed — had almost no way to act on it.

Initial Problem

Heights ran email the way most subscription brands do: reliable, well-designed, and entirely static. The billing reminder went out on schedule, told the subscriber a charge was coming, and did nothing else. It was the single most-opened email in the lifecycle and the least commercially productive.

That left the team with a familiar set of constraints:

• The billing reminder did exactly one job. The highest-intent email in the subscription lifecycle existed purely to deliver a notification — no offer, no path to spend more, no reason to engage.
• Every upsell meant leaving the email. Adding a one-time product to an upcoming order routed the customer out to a portal or a product page. Each additional click cost conversions, so upsells stayed a low-yield afterthought.
• Static email gave the team nothing to iterate on. Without in-email actions, there was little to measure and less to optimize. Campaigns went out, and the team was largely guessing at what moved.

Zaymo’s Solution

Rather than build a new campaign, Heights made the email it was already sending do more. The billing reminder already reached every subscriber at the exact moment their next order was top of mind. Zaymo made that moment actionable.

• One-time add-ons, added in one tap. Interactive product blocks let subscribers append a one-time item to their upcoming order directly inside the email — no portal, no product page, no re-authentication.
• The offer lands at peak intent. The days before a charge are when a subscriber is already thinking about what’s coming. Presenting an add-on in that window converts far better than the same offer sent cold.
• No new sends required. The lift came from an email Heights was already sending to every subscriber, which meant no added send volume and no new deliverability risk.

The framing mattered as much as the mechanic. The add-on wasn’t positioned as an upsell — it was positioned as a convenience, a chance to adjust an order the customer already had coming.

Setup

Heights kept the implementation deliberately narrow:

• Placement. Zaymo’s interactive product blocks were added to the existing Klaviyo billing reminder flow, not a new campaign.
• Mechanic. One-click addition of a one-time product to the upcoming order — written straight to the subscriber’s next order in Skio — completed entirely in the email.
• Audience. Active subscribers with an upcoming charge — the full billing reminder population.

The figures below reflect roughly a month of the interactive billing reminder running as an A/B test against a standard control.

Results

Heights’ base is unusually concentrated — a near-cult following around one flagship line (Vitals), with a set of natural add-ons like magnesium sitting right alongside it. That’s fertile ground for an in-email add-on, and the numbers reflect it:

Takeaways

The most valuable real estate in a subscription program is usually already in the send calendar. Heights didn’t add a campaign, buy more traffic, or increase send frequency. It took the one email every subscriber reliably opens — the billing reminder — and gave it something to do.

The broader lesson is about friction, not offers. Heights’ upsell offer wasn’t new; the ability to accept it in one tap was. As long as adding a product meant leaving the email, the offer converted like an afterthought. Removing the round trip is what turned a notification into the highest-yield revenue moment in the lifecycle.