A constituent completed their registration, but didn't add and purchase an upsell during the process that they intended to. Can an upsell be added to a registration after the registration has been completed?
To accurately associate upsells with the registration, the upsell has to be added prior to completing the registration. In order to associate an upsell after registration has completed, you will need to unregister the participant and refund Registration. They can then re-register with the intended upsell association.