Customer is using Mollie payments for WooCommerce which Robot Ninja doesn't support off the bat: https://wordpress.org/plugins/mollie-payments-for-woocommerce/

With 30k downloads from .org, it appears this extension is fairly popular across the EU!

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After a brief look into it, Mollie payments for WC offers many different integrations with other gateways (i.e. PayPal was the most known from their list).

Any mollie gateway on the checkout will have payment method IDs like payment_method_mollie_wc_gateway_{Payment_ID} so if we look at supporting for standard WC PayPal, we'll also need to add support for mollies own PayPal separately.