Client id must have been created by gtag.js?

[8ctopus]

I have found this in the google doc:

In order for an event to be valid, it must have a client_id that has already been used to send an event from gtag.js. You will need to capture this ID client-side and include it in your call to the Measurement Protocol. In send an event to your property, we use "client_id" as the client_id. You will need to replace this with a real client_id that comes from gtag.js.

Does your practical experience corroborate the quote or not?

If affirmative, I think it should be added to the doc.

I'm adding the stackoverflow question that made me think about this if you're interested https://stackoverflow.com/questions/69105735/google-analytics-4-measurement-protocol-api-used-without-gtag-js-or-firebase

[aawnu]

It is already in the documentation that you 'should' use the gtag identifier.

• https://github.com/aawnu/php-ga4#data-flow

It is entirely possible to use custom identifiers if you rely solely on server side tracking, but the gtag id will ne necessary for the auto-collected information.

[8ctopus]

Thank you.