Problem summary
You can see estimated Google Analytics 4 (GA4) values in Funnel instead of complete event counts when GA4 samples a request.
Error message or symptoms
The Samples read rate value is below 100%.
Funnel and GA4 totals differ because one result uses sampled data.
Values change when you request a different date range or set of fields.
When does this occur
The number of events in a request exceeds the quota for the GA4 property.
GA4 processes only part of the available events and scales the result.
Root cause
GA4 samples data when a report, Exploration or API request exceeds the property quota. Google uses part of the events to estimate the complete result. Funnel automatically reduces the download interval to one day to lower the risk of sampling, but GA4 can still sample large requests.
Solution
Add the Samples read rate dimension to the Funnel data source.
Check the value for the affected dates. A value of 100% means that the data is not sampled.
Treat values below 100% as estimates. For example, 75% means that GA4 estimated the result from 75% of the events.
Compare Funnel only with a GA4 result that has the same sample rate and request fields.
For details, see Google's About data sampling.