Characteristics causing recurring payment error

I'm using Hikashop starter, akeeba subscriptions, akeeba/hikashop plugin and paypal recurring. Recurring payments were working fine - I can associate a subscription with a product and payment goes through. But if I add a Characteristic to a Product I get this error from paypal: "Invalid Regular period. You must specify valid values for the A3, P3 and T3 parameters for a subscription." If I take away the characteristic it works again.

Is this a bug or a set up problem for me? Any pointers much appreciated.

I gather the values mentioned in paypal represent: A3 = Price, P3 = Subscription Duration, T3 = Subscription Duration Units
So it must be causing a change in one of those values, but since characterstics don't change the price, I don't know what it can be.

Hi,

A3, is the order full price. So it's not related on the price of the variant.
P3, is the product_subscription_id so you can check in your variants if the subscription level is set.
T3 is automatically generated in the plugin, the error should not come from here.

I think that the subscription level is not set in your variants.