Once the newsletter has been signed up for, players should receive a code to unlock the shoes. So long as you correctly input your email and platform you’ll be playing Sonic Frontiers on, there should be no issues.

And that’s it. Once the code has been entered the Soap Shoes are accessed through the main menu under the “Extras” tab. Once in the “Extras” menu, go to “Sonic Outfits” and select “Sonic Adventure 2 Shoes.”

Source: https://www.distractify.com/p/how-to-get-soap-shoes-sonic-frontiers