Upsells in LCRM are essentially donations that are made to a specific designation. In Luminate CRM, the upsells are not tied to the TeamRaiser Registrations. The Related Transaction field is meant for the registration fee to be selected. You can manually set the Upsell Amount in the registration as a reference to the additional "gift" that they made, but that field is technically not linked to the Upsell donation.