surendranb / compatible-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."
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 ordate/deviceCategory/geo dimensions — not with session campaign dimensions.