There are four Add-On reference types:
1- Channel Add-Ons:
If the add-on is automatically created according to your rate plan on your website or received from channels, it will be listed as Channel Add-ons.
2- Admin (Rate Plan) Add-Ons:
If a booking has been created manually and its add-on comes from a rate plan, it’s called an Admin (Rate Plan) Add-on.
3- Admin (Manual) Add-Ons:
If the user adds any add-on to the created booking, it’s known as an Admin (Manual) Add-on. 
4- Upsell Add-Ons:
If add-ons come from the confirmation process (by guests), they are listed as Upsell Add-ons.
