Maybe you weren't logged in/you were logged into a different itch.io account? This page https://itch.io/docs/buying/already-bought has advice on this, or you can just look for an email from itch.io (sent to the same email address that's connected to your Paypal account). They should have emailed you when you made the purchase, and it will contain a link to the downloads.
Was it for "The Hero's Journey (full game)" or "The Hero's Journey (NSFW edition)"? The former would give you the files for this version of the game:
https://maneki-mushi.itch.io/theherosjourney
(this version doesn't have the NSFW content, but the purchase would have unlocked the booklet)
If it was the latter you would have been able to download the NSFW edition of the game, but not the booklet.
