Also called: event parameters, GA4 parameters, custom dimension
GA4 collects some parameters automatically (page_location, page_title, language) and accepts custom ones you define. Custom parameters must be registered as custom dimensions or metrics in the GA4 admin before they appear in standard reports — unregistered parameters are collected but invisible outside BigQuery export and some explorations.
Types matter. A purchase value sent as the string "74.50" instead of the number 74.50 will not aggregate as revenue, and the report shows zero rather than an error. Currency must be a valid ISO 4217 code or the value is discarded.
GA4 enforces limits: 25 parameters per event, 50 custom event-scoped dimensions per property. Both are easy to hit on e-commerce sites, and exceeding them drops data silently.
Parameter-level bugs are the hardest kind to see: the event count looks perfect on the dashboard while the number attached to it — the revenue — is wrong or missing entirely.
It almost certainly has not been registered as a custom dimension in Admin › Custom definitions. Registration is not retroactive, so data collected before registering will not appear in standard reports even after you add it.
Up to 25 per event. Automatically collected parameters count toward related limits, so complex e-commerce events run out of room faster than the number suggests.
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