<b>Q: I registered a custom dimension but it shows '(not set)'. What did I miss?</b>

<b>Q: I registered a custom dimension but it shows '(not set)'. What did I miss?</b>

A: Registering the dimension and <i>sending</i> the parameter are two separate steps.
— Confirm the event actually carries the parameter: use DebugView (Admin → DebugView) and click the event; your parameter must appear in the list.
— The scope must match: an event-scoped dimension reads an event parameter; a user-scoped one reads a user property. Mixing them gives '(not set)'.
— Names are case-sensitive and must match exactly between your tag and Admin → Custom definitions.

Also: data only populates going forward, never retroactively.

TL;DR: '(not set)' = parameter not sent, wrong scope, or name mismatch. Verify in DebugView first.

Got a GA4 question? Drop it 👇