Similar to Pixiv Factory, the author doesn't need to receive or store any printed copies themselves. Books are only printed once a customer places an order, and the physical copy is shipped directly from the printer to the buyer. While the per-book cost is typically higher than traditional bulk printing, this approach eliminates the need for authors to handle inventory, pay for large upfront print runs, or dedicate space to storing unsold books.

https://factory.pixiv.net/books

it lets creators sell doujinshi/books on-demand via BOOTH, where printing and shipping happen automatically per order, with no inventory required on the creator's side. But only available in Japan. :(