Sumup payment form not appearing in custom order

Hi,
I’m working on a woocommerce shop in wich the sumup plugin work good, but I have an issue when it comes to orders generated by the admin (directly by the “add order” option or via plugins like “phone orders”).
When the customer receives the order email with the checkout link, it is possible to pay with other payment method (paypal, bank transfer and so on) but not SumUp. The SumUp part of the checkout page shows only the message “Pay with your credit card via SumUp” and no form to insert credit card data is loaded.
Is this a bug or do the SumUp plugin for woocommerce is not supported for admin-generated orders?