There are a number of reasons why this problem could occur.

Print template is missing

To check whether a print template has been set, go to Settings → Print templates in the checkout. If there is no template here under 'Subscriptions', please add one. Look here or ask Partner Management to do this for you.

Also check in the Admin whether the template has been set for the pricetype. To do this, go to Settings → Tickets → Price types and select the relevant subscription. Check in the right-hand column ('advanced') whether the correct template is set at 'POS print template'.

Subscription is sold outside validity

In the Admin, go to Settings → Subscriptions → Subscription templates, and select the relevant subscription. Check the validity here. If this is in the past or future, the subscription cannot be printed.