Codisto LINQ uses cookies to store data. In the ecwid admin those cookies are third party. If you have third party cookies blocked in your browser you will see the following error when attempting to access Codisto LINQ:

 

Enabling third party cookies

Google Chrome

Navigate to chrome://settings/ > Content Settings > Cookies

Ensure "Block third party cookies" is not enabled

Other browsers

Navigate to the privacy settings for your browser and ensure third party cookies are allowed.