No, there is not a way to credit a WotC book purchase toward content on the Roll20 platform. When you buy a WotC-licensed product on the Roll20 marketplace, you are paying not only for the content but the effort to put it into Roll20: the compendium entries, the charactermancer integration, etc. Money doesn't flow from WotC to Roll20 because a user decides to use a book's content on the platform. Each WotC product format available, whether book, Roll20, D&D Beyond, or others is separate. A customer must purchase each format they wish to use. That being said, the digital formats like Roll20 allow you to type anything into the system. So you can just type the features directly into the character sheet.
