Hello ​@EmilHH 

The issue of missing leads in Klaviyo from Facebook Lead Ads can be due to incorrect integration settings, unmapped forms, duplicate emails, invalid submissions, or syncing delays. Verify the integration is active, reauthorize Facebook, and ensure the correct Lead Ad form is linked. Check for duplicates or leads requiring double opt-in confirmation. If field mapping or API errors persist, manually upload leads as a temporary solution. For detailed troubleshooting or implementation, feel free to reach out.

Hi ​@EmilHH 

It can sometimes take Facebook up to 24 hours to process profiles synced from Klaviyo. If your custom audience does not have as many profiles as you expected, make sure that you've given Facebook 24 hours to fully process all of the profiles from your sync.

Alternatively, it is likely that a percentage of the email addresses you attempt to sync will not match with an existing Facebook account. This is why your Facebook Custom Audience size may be smaller than the linked list or segment in Klaviyo. Facebook will not return an error, but won't add any contacts who have email addresses that don't match to an existing Facebook account.

One troubleshooting step you can take is to try syncing the same list in Klaviyo to a new custom audience by selecting + Add Custom Audience sync (under Custom Audience Settings) on your Facebook Advertising Integration settings page.

Once you've selected the list or segment and audience for your new sync, click Update Settings. 

Hope this helps! 

Hi ​@EmilHH 

Thank you for posting in the Community!

The issue where not all leads from Facebook Lead Ads are making it into your Klaviyo list can arise for several reasons. Here’s a step-by-step guide to troubleshoot and resolve the problem:

Step 1: Verify the Facebook-Klaviyo integration:

1. Check integration status:

   • Go to Integrations in Klaviyo and locate the Facebook Lead Ads integration.
   • Confirm it is active and authenticated with the correct Facebook account.
   • Re-authenticate if necessary, ensuring you have the correct permissions.

2. Review lead form mapping:

   • Ensure all lead forms in your campaign are properly mapped to the Klaviyo list.
   • Double-check that the fields (e.g., email) are correctly assigned during the setup process.

Step 2: Account for Facebook processing time:

• Facebook processing delays:

  • Facebook can take up to 24 hours to process profiles synced from Klaviyo. If your custom audience or Klaviyo list doesn’t have the expected number of profiles, wait for a full 24 hours to allow Facebook to sync all the data.

• A potential solution: 

  • You can try to setup a integration with make.com, where you use the modules: Facebook Lead Ads and Klaviyo. That will sync all of the subscriber over to your list. 

Hope that helps or else, let me know! :-) 

Christian Nørbjerg Enger
Partner & CPO
Web: Segmento.dk
LinkedIn: @christianfromsegmento
Voldbjergvej 22b, 8240 Risskov

Hi ​@EmilHH!

Thanks for the question. MANSIR2094 mentioned that this issue may be due to double opt-in, and I wanted to echo that. When leads sign up through a Meta ad, they’re synced to the list in Klaviyo you specified. If that list is double opt-in, these leads will be sent a confirmation email asking them to confirm they’d like to be added to the list. They will not be added to the list until they press the button to confirm their subscription in that email.

Since 12 of 27 people who filled out the lead ad have been added to the list, it does appear that the connection between Klaviyo and Meta is healthy, because the list is still collecting leads. I’d recommend going to the list’s settings, then navigating to the consent tab, and seeing if the list is double opt-in. If it’s not, feel free to reach out to our support team, and we can take a closer look into this!

Hello Emil, it’s a common but frustrating issue when your leads from Facebook Lead Ads don’t fully sync with Klaviyo.

The connection often doesn’t work perfectly right out of the box, as you've noticed with the difference between 27 sign-ups and 12 people on your Klaviyo list.

The most likely causes are a combination of factors, which the others in the thread have touched upon.

These include integration misconfigurations, like the wrong lead form being mapped or incorrect field assignment, and syncing delays, where it can take Facebook up to 24 hours to process all profiles.

A crucial point is the list's consent settings - if your Klaviyo list is set to double opt-in, leads will receive a confirmation email and won't be officially added to your list until they click the link inside it.

The fact that 12 of 27 people did make it suggests the primary connection is working, but it may be a mix of double opt-in being active and other minor data errors preventing the rest from appearing.

Leads with invalid or duplicate email addresses can also be dropped.

For a more robust and reliable solution that bypasses many of these common integration errors and improves data quality, you should consider using a setup involving the Klaviyo API in conjunction with the Facebook Conversions API (CAPI).

Implementing this via Google Tag Manager (GTM), often with a server-side tagging solution like Stape or Google Cloud Platform (GCP), provides a far more complete and accurate lead tracking system than the default integrations.

Here’s why this advanced setup is better: the default Facebook-Klaviyo integration can be unreliable because it relies on older, less direct methods of data transfer.

By contrast, the Klaviyo API lets you directly and instantly send lead data from your own server-side environment into Klaviyo, ensuring that sign-ups are added immediately and correctly, which eliminates many of the syncing delays and common integration breaks.

The key component for improving your overall Facebook advertising performance is the Facebook Conversions API.

Instead of relying solely on the browser-based Facebook Pixel, which can be blocked by ad blockers or restricted by privacy settings like Apple's Intelligent Tracking Prevention (ITP), CAPI sends key customer actions, like a successful sign-up (a Lead event), directly from your server to Facebook's server.

This direct server-to-server connection is more reliable and less susceptible to data loss.

The Lead Standard Event is crucial here, as it tells Facebook exactly when a lead converts, allowing Facebook's algorithms to optimize your campaigns much more effectively by accurately seeing which ads generate the most quality leads.

To make all this work, you use Google Tag Manager to manage the data flow.

You configure GTM to capture the lead information (like email address) when someone successfully signs up.

For maximum reliability, you would use a server-side container in GTM, hosted on a platform like Stape or Google Cloud Platform.

This server-side tagging setup allows you to process the data securely and then send it out to both the Klaviyo API and the Facebook CAPI.

This ensures two things: first, that Klaviyo gets the lead directly and reliably added to the correct list; and second, that Facebook receives a clean, unblocked Lead Standard Event via CAPI, leading to better ad optimization.

This comprehensive approach is more resilient, accurate, and scalable for serious lead generation campaigns.