To make "sold-out" function working, you should change :

if($product->soldout() != ''):
by
if( (string)$product->soldout() ):
in snippets/products.php, line 21

otherwise '0' is consider as true.

Maybe I'm getting this all wrong, but there seems to be something wrong with the ht, tax etc. calculations:

Calculation of net price from ttc should be:

function cart_ht($ttc, $vat) {
	$ht = $ttc / (1 + $vat/100);
	return $ht;
}

Calculation of vat value to be added to a net price (this is probably what you need in your plugin if tax is set to true, but then the product prices should be net prices, because this value is added when I click the Paypal submit button; even though the text says "TVA incluse"):

function cart_vat($net, $vat) {
	$tax = $net * $vat/100;
	return $tax;
}

Calculate amount of tax included in a given TTC price:

function cart_vat_incl ($ttc, $vat) {
  $ht = $ttc / (1 + $vat/100);
  $tax_incl = $ttc - $ht;
  return $tax_incl;
}

Will you update this one for Kirby v3?

BTW good job with this one, love the simplicity

Few questions here:

• What's the current status of cartkit? any roadmap?
• Can you add the status to the top of the README.md file?
• How likely you are to discuss new features? (here's where the roadmap comes in handy).

Feature request: recurring payments for selling services.

Hi! documentation is down. I really need to read it.

Best regards, amazing plugin!

https://forum.getkirby.com/t/postage-function-with-paypal/8608