GA4 Measurement Protocol: the limits that silently drop your events

The Measurement Protocol lets a server send events to Google Analytics 4. It is simple to call and easy to get silently wrong, because the collection endpoint answers with a success status even when it discards what you sent.

Validate with the debug endpoint

Send the same body to /debug/mp/collect to get validationMessages back. RELAXED validation (the default) reports real errors. ENFORCE_RECOMMENDATIONS also turns recommended fields into errors. For example, once a device object is present it demands device.model, which a desktop browser cannot provide.

Limits worth enforcing before you send

• Up to 25 events per request and 25 parameters per event.
• Event and parameter names up to 40 characters; parameter values up to 100 characters.
• timestamp_micros at most 72 hours in the past. Older events are rejected.
• Parameter names may not start with _, firebase_, ga_, google_ or gtag.

Make server events join the browser session

Use the client_id from the _ga cookie and the session id from the _ga_<container> cookie, and include engagement_time_msec. Without them, server events appear as separate users and sessions, and may not show in standard reports.

Deduplicating purchases

GA4 deduplicates purchases with the same transaction_id, so always set it to your order id. It is the safety net if a purchase is ever sent twice.