Vendo OfferChange is equivalent to NATS PackagePlus. Please check NATS documentation to set this feature.
Not using NATS?
Redirect the user to the ChangeOffer URL which is documented here.
Once the client accepts the terms of the new offer, we will post a ChangeOffer callback to your callback_url so you can handle the upgrade or downgrade.
The ChangeOffer callback is documented here.
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