Switching Subscription works with PayPal but not with Paymill (down-/ upgrade)

With Paypal it is possible to switch a WooCommerce Subscription (https://docs.woocommerce.com/document/subscriptions/switching-guide/). That is to down-, up- or crossgrade a subscription. Under “My Account” > Subscriptions > Subscrition item there is a button visible to the customer. If Paymill is used as payment method (instead of Paypal) then this button is missing.

Is subscription switching not supported by the Paymill plugin?