I use react-ga4 in a React web app to send events to Google Analytics. An API call is also triggered on the backend for each event, so I have a server-side count of how many times this action really happens.

I’m seeing that the Google Analytics event count is consistently about 40% lower than the API call count. One guess is that privacy-focused browsers (like Brave) or ad blockers are preventing GA calls. However, it seems unlikely that 40% of my users are on such browsers or using those blockers.

• What else might cause such a discrepancy?
• How can I verify if privacy/ad-blocking is the real source of the difference?
• Are there recommended approaches or best practices to reduce this discrepancy and ensure the event tracking is as accurate as possible?