How to Link Additional User Data to Initial CompleteRegistration Event

Facebook Conversion API
1

In our web app, we trigger a sign_up or CompleteRegistration event as soon as a user enters their email. However, other critical details for Meta’s Advanced Matching and Google Enhanced Conversions—such as phone, first name, and last name—are collected later in the user flow.

Is there a way to send this additional data afterward to Google and Meta so that it links to the initial CompleteRegistration event or user account, enhancing data accuracy? Specifically, I’d like to ensure Meta can recognize and match these details retroactively. Also, is it sufficient to send this data only once to benefit from Enhanced Conversions and Advanced Matching, or is additional configuration needed to associate it with the user account on Google/Meta’s side?

Note: We send all events within our SPA directly via JavaScript with GA4—no Tag Manager or Facebook Pixel is used.

Is the following sequence the correct approach?

  1. Trigger the sign_up event (or CompleteRegistration for Meta).
  2. Wait until additional data is entered.
  3. Send a single, custom event with the added data to Meta CAPI and GA4/GAds.

Would this be the correct way to ensure all relevant data is captured and matched?

Any insights or best practices on this would be highly appreciated!

2

There are no means to retrospectively append data to an already sent event.

Is the following sequence the correct approach?

  1. Trigger the sign_up event (or CompleteRegistration for Meta).
  2. Wait until additional data is entered.
  3. Send a single, custom event with the added data to Meta CAPI and GA4/GAds.

this looks like a most straightforward approach to me, yes.

3

Thank you for the clarification. For the sake of completeness, I’d like to mention that Google Enhanced Conversions indeed supports this through what they call Conversion Adjustments: Google Ads Conversion Adjustments.

Whether this is useful for my specific use case or if it brings any real benefit is another question entirely.