Parameter for Gumroad license API changed

[kristinbaumann]

Hi!

First: Love this toolkit! 💚

I found the following issue: The Gumroad license key verification API changed in January.

From the Gumroad website:

⚠️ Important: Our license key verification API now requires the product_id parameter instead of product_permalink for all products created on or after Jan 9, 2023.

This affects the two monetization utilities validateGumroadLicenseKeyMainAsync and validateGumroadLicenseKeyUiAsync since the wrong parameter is passed to Gumroad for new Gumroad products.

I am happy to contribute with a PR if wanted.