Why are subscription swaps failing?
Why are customers unable to swap products?
There are a few reasons why customers might be unable to swap products:
The customer is using a different currency than the store's default currency.
The products don't belong to the same subscription group.
They have a prepaid subscription. Only an admin can swap for prepaid subscriptions.
Read more about how to swap a product in a customer's subscription in Subscription Management: Merchant Perspective.