PayPlans subscribe to additional plan

We use payplans to pay and register to easysocial. When user is subscribed to a plan and registered if the user tries to subscribe to another plan by going to plan url (smth like index.php?option=com_payplans&view=plan&task=subscribe&plan_id=3&group_id=0 ) the plan details are not displayed, but instead user ends up on confirm invoice page.
Can you please assist.