The store has been configured and validated, you can now go back to the main page to continue the process: Go Back
Unfortunately Shopify has changed the requirements for the way we used to access data. The new way is more involved to set up. You need to activate developer access on your account (no issues or harm associated with this). Then add a custom app, enable the appropriate permissions and enter the access token here.
Please note that you are entering the credentials on Shopify's web site (verify the URL and HTTPS certificate), your username or password is never shared with QuickSKU. We are given an authorization token from Shopify that is used to access your site. You can revoke our access at any time, but then our service won't work any longer for your Shopify store.
Link to go back to the app development settings: App development