Q: I send a custom parameter but it shows '(not set)' — what's the checklist to fix it?

Q: I send a custom parameter but it shows '(not set)' — what's the checklist to fix it?
A: Parameters must be registered as dimensions before reports can read them:
— Confirm the parameter actually arrives: DebugView → click the event → see your key (e.g. plan_type) in the params list.
— Admin → Custom definitions → Create custom dimension → scope 'Event', enter the exact event parameter name (case-sensitive).
— Wait up to 48h — historical rows before registration stay '(not set)'; they won't backfill.
— Build an exploration filtering on the new dimension to confirm values flow.
TL;DR: Verify the param in DebugView, register it under Custom definitions with the exact name, then wait — past data won't backfill.
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