checkout.js

$( 'form.checkout' ).on( 'change', 'input.qty', function( e ) {
		let maxQtyData = {};

		let inputs = $( this ).closest( '.woocommerce-checkout-review-order-list' ).find( 'input.qty' );

		inputs.each( function( index, element ) {
			maxQtyData[$( element ).attr( 'name' )] = $( this ).attr( 'max' );
		} );

		var data = {
			security: wc_checkout_params.update_order_review_nonce,
			action: 'update_order_qty_review',
			order_data: inputs.serialize(),
			max_data: maxQtyData
		};

		if ( timeout !== undefined ) {
			clearTimeout( timeout );
		}

		timeout = setTimeout( function() {

			$.ajax( {
				type: 'POST',
				url: wc_checkout_params.ajax_url,
				data: data,
				success: function( response ) {
					$( document.body ).trigger( 'update_checkout', { update_shipping_method: true } );
				}
			} );
		}, 100 );

		return false;
	} );
} );