In the case of personalized products, the code snippets (Link) provided by Klaviyo may not work. To solve this issue you need to add the following code snippets after the Klaviyo 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.