Some traffic has unfilled FB subs

If some of your traffic arrives with unfilled subs, look at the browser: such clicks are usually opened in Chrome rather than inside the FB / Instagram app.

The reason is that some link-opening flows on Android bypass the macro expansion mechanism. In these cases Meta renders the ad but opens the URL outside the full click redirect pipeline.

This most often happens in the following scenarios:

• Instant Experience

• opening links in an external browser (external browser preference)

• Android intent optimization

• Chrome Custom Tabs

• deep links

• Reels / Stories edge cases

As a result, the static query parameters in the link are preserved, while dynamic substitution is not performed — the subs arrive empty.

This is a known instability on Meta's side — there is nothing we can do about it from our end.

What to do

• Account for the share of such traffic in your analytics: some clicks will always arrive with empty subs — this is not a campaign setup error.

• Use static sub values where possible: they are preserved even when dynamic substitution does not fire.

• Do not build critical logic (attribution, traffic distribution) solely on dynamic substitutions — provide a default behavior for clicks without parameters.