Mollie

Mollie has no cloud storage of products, you need to manage them in Kirby.
It does not collect the email on it's hosted checkout, thus you need to provide the email manually to allow for automated accounts creation.
You can not sell products with automated tax calculations unless you extend the providers yourself.

Using the provider

<?php

return [
   'bnomei.kart.provider' => 'mollie',
   // other options
];

API Credentials

MOLLIE_SECRET_KEY=XXX

Customzing the Checkout

You can use callbacks to customise both the checkout process and each line item. The returned arrays from your callbacks will be merged with the defaults created by the plugin for this provider, allowing you to override those defaults. Check the relevant PHP class and the linked online documentation for the provider to learn more about the expected data structure.

<?php

return [
    'bnomei.kart.mollie.checkout_options' => function (\Bnomei\Kart\Kart $kart) {
        // configure the checkout based on current kart instance
        // https://docs.mollie.com/reference/create-payment
        return [];
    },
    'bnomei.kart.mollie.checkout_line' => function (\Bnomei\Kart\Kart $kart, \Bnomei\Kart\CartLine $line) {
        // add custom data to the current checkout line
        return [];
    },
    // other options
];

Automated Account Creation

The hosted checkout from Mollie does not have a custom field to collect your customer's email address. The Kart plugin has two ways to deal with this. It will work directly if your customer has a Kirby user account and is logged in. Kart will then forward the email address of the Kirby user account. The other option is to supply the email address as a form field/parameter within the checkout, as in adding a simple <input type="email" name="email">.