The normal thing is, that you get an email from Paypal and an email from Itch, around the same timestamp.
One is Paypal informing you about the payment made and the other from Itch mailing you your download link. The mail title should read "Your purchase of 'The Choicer Voicer' and is sent from support@itch.io
Do a full text search of both your inboxes for the term "purchase" and triple check your mail settings on Itch. You can add your paypal address on https://itch.io/user/settings/email-addresses
Additional emails
You can link additional email addresses to your itch.io account in order to get access to anything purchased under those email addresses. For example, your PayPal email address might be different than your regular email address so you'd want to add it as an additional email.