It is always easier to sell more things to existing customers than it is to find new customers.
There are several ways to encourage customers to buy more stuff. The three most widely used on DTRPG are:
Bundles encourage cross-sales by giving a discount for buying the complete bundle. DTRPG is smart enough to reduce the price of the bundle if people already own some of the included titles.
Footers let you show other titles you think may be of interest, and link to them. The problem with footers is that they are way down the page, and may never been seen. They also do not offer any incentive to buy more.
Emails let you tell existing opted-in customers about new titles. You can give discounts and show off what the new title has to offer. You can also habitually link to other titles that are related to the main title you are showcasing. But, not everyone opts-in for email, and not every email gets read.
What I have done in the two supplements shown in this video is include a discount link in the actual text of the first supplement, pointing owners to the second title.
So far, that discount link has been used 26 times. That is halfway to Copper best-seller level.
That link can stay there forever. It is on the final page of the PDF and owners can come back at any time and pick up the second booklet.
The product page on the second booklet points people to the first book in the pair, and brings attention to the offer.
I also did this with the Lowborn fanzine for Zweihander. As that was intended for print, I included QR codes. They were linked in the PDF, or could be scanned from the physical magazine.
This is not a killer application of discount links. How many people would have bought both titles even without the discount link I couldn’t say. But, it definitely makes buying the second book easier for people who own the first.
Making things easier is aways good. We don’t want to put barriers in the way.