In a fragmented advertising landscape, marketers are constantly challenged to prove ROI — especially as more conversions happen outside the view of traditional tracking pixels. Enter Conversion APIs (CAPIs): the unsung hero of modern media measurement.
The Problem with Traditional ROAS Measurement
Return on Ad Spend (ROAS) has long been the go-to metric for marketers, but it’s typically limited to what JavaScript tags and cookies can see, which are mainly online transactions. That works well for ecommerce, but falls apart in industries like travel & hospitality, retail, and finance where conversions often occur offline, over the phone, through affiliates, or in-store.
These “unobservable” events — like OTA bookings for travel or in-store purchases for retail — don’t get counted in your ROAS unless you push them into your media platforms and tie them to an advertising campaign.
As a result, you’re doing all the work but only getting credit for half of it. This attribution gap can have significant consequences for growth down the line as teams look to invest into what’s working, and move away from what’s not.
How Conversion APIs Fill in the Gaps
CAPIs allow you to pass conversion data directly from your own Customer Data Cloud (CDC) systems to media platforms such as Meta, The Trade Desk, or TikTok. This server-to-server connection means:
You can include offline and online conversions, even if JavaScript can’t fire.
Media platforms can use this data to optimize targeting and suppress ads to converted users.
You get a more accurate and comprehensive view of what your ad dollars are actually delivering.
Here’s a real world example. A marketer wanted to more accurately track in-store transactions via a Meta CAPI to measure the full cross-channel impact of their campaigns. Once implemented, the CAPI registered a 75% lift in tracked conversions — showing the full breadth of the impact of its Meta campaigns. Without the CAPIs, all of those in-store transactions would have gone un-attributed to their campaigns.
Is It Hard to Set Up? Not Anymore.
The best part: CAPIs are easier to implement than many assume. Most platforms don’t charge to use them, and many brands already have the infrastructure in place (via CDCs) to start sending these signals immediately. In fact, for many, it’s low-effort, high-return work.
While legacy ad tech providers may add cost through per-event tolls, modern setups are often free or low-cost. And with the ability to turn around updates in under an hour, CAPIs also enable campaign optimization and smarter budget allocation.
Bottom Line
If you’re still relying solely on pixel-based tracking, you’re flying blind — and likely underreporting your marketing impact. CAPIs offer a simple, effective way to unlock the full value of your ad spend, improve consumer experiences, and defend your marketing budget with confidence.
There’s no good reason not to do it. Start now. The data (and your CMO) will thank you.
Watch our webinar on unlocking more comprehensive ROAS to learn more about measuring the full impact of your advertising spend.
If you’re an Amperity customer and want to get started with CAPIs, speak with your Customer Success Manager.