Move the Global site tag (gtag.js) into a page top rule as Sequential HTML. Note that the script that it loads is async, so there really is no performance issue here. Be sure to replace DC-XXXXX (in two places) with your account ID.
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<!-- Global site tag (gtag.js) - DoubleClick -->
<script async src="https://www.googletagmanager.com/gtag/js?id=DC-XXXXX"></script>
<script>
window.dataLayer = window.dataLayer || [];
function gtag() {
dataLayer.push(arguments);
}
gtag('js', new Date());
gtag('config', 'DC-XXXXX');
</script>
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The script above does four important things.
1) It establishes window.dataLayer as a native javaScript array. This should be done as early as possible in case other code in the page render lifecycle need to push data into it.
2) It establishes the gtag function so that your code, later on, can call it.
3) It pulls down the (generic) gtm library asynchonrously.
4) It establishes your account id(s). You might have a few depending on what Google services you are using.
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For the event snippet, I'd suggest adding just the JS portion as a "non-sequential JS" tag on your DTM event rule.
gtag('event', 'conversion', {
'allow_custom_scripts': true,
'u1': _satellite.getVar('Product Display Name'),
'u2': _satellite.getVar('Product Model Code'),
'send_to': 'DC-XXXXX/invmedia/y9sjx4y9+standard'
});
