Your HTML snippets — both the <script> in head and the <noscript> in body
job
Loads the GTM container on your site so Tag Manager can fire all your tags
where to find it
GTM Dashboard
→
Admin
→
Container Settings
≠
Measurement ID
G-XXXXXXXXXX
G-
identifies a GA4 property
XXXXXXXXXX
your unique property ID
goes into
The GTM tag configuration — the Tag ID field inside your Google Tag setup in GTM
job
Tells GTM which GA4 property to send data to when the tag fires
always confirm from here — not any other screen
GA4 Admin
→
Data Streams
→
Your stream
→
Measurement ID
⚠️
The most common mistake: GA4 shows Measurement IDs in multiple places during setup. Always confirm from Admin → Data Streams → your stream. IDs from other screens can silently point to the wrong property.