In the case of personalized products, the code snippets (Link) provided by Klaviyo may not work. To solve this issue you can use the following code snippets instead of the provided snippets.

<script type = "text/javascript" >
window.pplr_custom_cart_track = function(data) {
var klAjax = true;
var _learnq = window._learnq || [];
var cart = {
total_price: data.total_price / 100,
$value: data.total_price / 100,
total_discount: data.total_discount,
original_total_price: data.original_total_price / 100,
items: data.items
}
if (item !== 'undefined') {
cart = Object.assign(cart, item)
}
if (klAjax) {
_learnq.push(['track', 'Added to Cart', cart]);
klAjax = false;
}
}
</script>

Make sure you fulfill all the prerequisites (Link) by Klaviyo before adding the snippets.