I had the same problem happening to me, turns out you need to have more than $10 spent, I had exactly $10 and couldn't do it, so I bought something else and now it's available! hope this works for you too
I'm pretty sure I spent $10 on itch.io, but the option is still not available. I don't know if that has anything to do with the fact that I used two different email addresses. But all the purchases are linked to this account.
Thanks for getting back to me. I confirm that I made two purchases with two different amounts that should add up to more than $10. Is the option only available if you have made a single purchase on itch.io of $10 or more?
I believe it’s because you bought the item 3 years ago under a different email, so although your account “owns” the purchase, it did not “buy” it. I’ve attached it do your account so you should be within the threshold now.