I would think of it three different ways:
1. Money going into your book. So things like software to write your book or edited or design covers for format I would probably start there.
2. Money to support your book. This would be subscriptions for building your author platform, Medium Substack, those sorts of things.
3. Money to lift your book up. This would be ads or promotions or connecting with influencers and getting sponsorships out for your book to point people to it and to get more eyes on it.

So it depends on where you’re at if you have the first one covered the first two covered then I would move to number three .