I just set up a new 1.5.8 ZenCart for an author. After battling with the MySQL Database Wizard for nearly half an hour, I finally got everything set up, and now I can access his new shopping cart.

He wants to use Square exclusively, so I went straight to Payment Modules first, disabled the default modules, and tried to enable Square. Following instructions, I logged into Square and found the Developer section (pretty much by luck since it's not part of their menu structure). I created a new application for his website, and configured the Credentials and OAuth pages. I copied the Application ID and the Application Secret into the Zencart module fields. It tells me the OAuth Redirect URL should be https://sitename.com/index.php?main_page=index, which is quite different from other urls mentioned in this thread, but I dutifully entered in on the Square OAuth page.

I can log into Square from the ZenCart module blue text link. But when I click the green link, it takes me to the new ZenCart's index page instead of into Square. Is that why I'm still getting an (Access Token needed) error message?

I appreciate any help you can give me on this!!