surendranb Compatible Dimension and Metric Combinations
GA4 enforces strict rules about which dimensions and metrics can appear in the same request. Incompatible combinations return a 400 error: "The request's dimensions & metrics are incompatible."
The core rule
GA4 data is scoped at three levels: event, session, and user. Mixing dimensions and metrics from incompatible scopes causes errors.
| Scope | Example dimensions | Example metrics |
|---|---|---|
| Event | eventName, customEvent:* |
eventCount |
| Session | sessionDefaultChannelGroup, sessionSource, sessionCampaignName |
sessions, bounceRate, sessionKeyEventRate |
| User | firstUserDefaultChannelGroup, firstUserSource |
totalUsers, newUsers |
Most common incompatible pairs
| Dimension | Incompatible metric | Use instead |
|---|---|---|
sessionSource / sessionMedium / sessionCampaignName |
eventCount |
sessions |
eventName |
sessions |
eventCount |
promotionId / promotionName |
most session/user metrics | only pair with promotionViews, promotionClicks |
itemId / itemName |
sessions, totalUsers |
itemsViewed, addToCarts, ecommercePurchases |
firstUserSource / firstUserMedium |
sessions |
totalUsers, newUsers |
When you hit this error
The GA4 error message names the exact field to remove:
"Please remove eventCount to make the request compatible for example."
Read the message literally — remove that field and replace it with a scope-compatible equivalent.
Safe combinations (always work)
date+ any metricdeviceCategory+ any metriccountry/city+ any metricpagePath/pageTitle+screenPageViews,totalUsers,sessionssessionDefaultChannelGroup+sessions,totalUsers,bounceRate
Ecommerce-specific
Ecommerce metrics (ecommercePurchases, purchaseRevenue, addToCarts,
itemsViewed) are event-scoped. Pair them with event-scoped or
date/deviceCategory/geo dimensions — not with session campaign dimensions.