In plain English
It exposes an event parameter or user property in reports. Sending a parameter is not enough; it has to be registered as a custom dimension before it appears anywhere.
There is a limit on how many you can register, and registration does not backfill history. Data only appears from the point it was registered onward.
What to know
Registered, not automatic
Sending the parameter is only half.
From parameters or properties
Event-scoped or user-scoped.
Limited number
Quotas apply.
No backfill
Data starts from registration.
Why it matters
The most common GA4 complaint, that a parameter is missing from reports, is almost always an unregistered custom dimension. It is a two-minute fix that cannot recover past data.
Common mistakes
×Sending parameters and never registering them.
×Registering dimensions with enormous cardinality.
×Expecting historic data to appear.
×Filling the quota with dimensions nobody uses.
FAQs
Why is my parameter missing from reports?
It needs registering as a custom dimension.
Will it show past data?
No. Registration applies from that point forward.
WRITTEN BY TARIQ SALLAM
Marketing Consultant. Entrepreneur. Content Creator.
I'm a marketing consultant, entrepreneur and content creator. I help businesses grow through practical marketing, websites, SEO, content and AI.
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