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AJAX call to Klaviyo API being blocked by browser's tracker-prevention

  • February 24, 2026
  • 2 replies
  • 74 views

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  • Contributor I

We have a newsletter signup form on our website that uses Javascript AJAX to make an API call to https://a.klaviyo.com/client/subscriptions/ to add someone to our newsletter list in Klaviyo.  We have noticed that sometimes if the user’s browser is configured to block trackers, it blocks this API request.  I found some other forum posts (e.g. this one) describing this happening when it actually is trackers (klclick1.com), but in our case it isn’t click-tracking at all, it’s just trying to send a request to the API.  Is there anything we can do to prevent API calls from being classified as trackers (without requiring users to change their browser settings)?

Best answer by Kim from Cadence

@a22,  client-side tracking for Klaviyo — and other analytics tools— can be unreliable. 

It sounds like you’ve created a custom form you’ve wired up to call Klaviyo’s client API API vs. using a Klaviyo native signup form (built in the Klaviyo UI), so this advice is for the former case. 

The best workaround would be to call an API endpoint you control and proxy these requests through to Klaviyo’s server-side subscription APIs. I’d avoid proxying to the client-side subscription APIs; these are intended to be called from a browser… there be dragons trying to simulate that with a proxy API. 


Hope this helps! 


Cadence / Book a demo

2 replies

Kim from Cadence
Partner
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@a22,  client-side tracking for Klaviyo — and other analytics tools— can be unreliable. 

It sounds like you’ve created a custom form you’ve wired up to call Klaviyo’s client API API vs. using a Klaviyo native signup form (built in the Klaviyo UI), so this advice is for the former case. 

The best workaround would be to call an API endpoint you control and proxy these requests through to Klaviyo’s server-side subscription APIs. I’d avoid proxying to the client-side subscription APIs; these are intended to be called from a browser… there be dragons trying to simulate that with a proxy API. 


Hope this helps! 


Cadence / Book a demo


Byrne C
Community Manager
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  • Community Manager
  • February 27, 2026

Hi ​@a22,

+1 to the server-side endpoint recommendation! Additionally, you might be able to reverse-proxy the call through your own domain. So instead of showing https://a.klaviyo.com/client/subscriptions, you’d show https://api.yourdomain.com/klaviyo-subscribe or something similar, so any tracker prevention service sees that the call is still coming from you.