When I try to cancel a subscription on my forum, the cancel button leads me to this error message on Paypal :
"The unsubscribe button you clicked through is invalid. You can find the status of all subscriptions in your transaction history."
Even if I cancel manualy on Paypal, it doesn't cancel on Xenforo (so I would have to do it manually for every user unsubscription).
Edit : more information
In the transaction history I see the message "Information: No txn_id. No action to take." in response to the cancel action on the Paypal account. I also see "txn_type" is "subscr_cancel", and "subscr_id" is not empty.