The person is trying to create a user_id in Google Analytics 4 (GA4) that is linked to Google BigQuery. They’ve used Google Tag Manager (GTM) to enhance GA4’s performance, linked GA4 and BigQuery, and successfully gathered site data in BigQuery. Then, they tried to pass user_id to dataLayer by adding a certain bit of code to the HEADER section above gtm.js. However, they’re unsure if using a string (USER_ID) at this stage may lead to incorrect results. They’ve also created a dataLayer variable and adjusted the GTM code accordingly.

Yet, the results they’ve received aren’t as expected. For instance, while they hoped to generate a specific comparison, the results turned out differently. They also anticipated the addition of a new user_id column in BigQuery, which hasn’t happened. It’s unclear whether they could be missing a step or overseeing something, or if it’s even feasible to pass the user_id from the frontend to the backend in the way they had envisioned.

They are seeking advice to clarify these concerns and any insights into their process would be highly appreciated.