Cannot redeem Store code - "You are not logged in."

Hi,

Thank you for posting your query in Microsoft Community and for your interest in Windows 10.

I can understand, how frustrating it can be, when things don’t work as expected.

We apologize for the inconvenience caused.

I'd be glad to help you.

Please answer the query, mentioned below:

• Do you login via Microsoft Account on your system? 

I would suggest you to login via Microsoft Account and check, if it works.

Please follow these methods, mentioned below to resolve the issue.
 
Method 1: 
 
Windows store Apps troubleshooter:  
 
The Modern app troubleshooter can automatically identify and fix some problems with apps and the Store.
   
Try to run the Windows store Apps troubleshooter, the steps are mentioned below:
 
 1. Type ‘Troubleshooting’ in the search bar and press Enter.
 2. Click on ‘View all’ on the left panel of the ‘Troubleshooting’ window.
 3. Click on ‘Windows store app’ and follow on the screen instruction. 
   
If the issue still persists, follow method 2.

Method 2: 

Please try to refer and follow the steps in the article, created by Babu V, replied on September 4, 2015, to fix your issue with Windows store on Windows 10.

http://answers.microsoft.com/en-us/windows/forum/windows_10-win_cortana/errors-when-running-cortana-windows-store-or-other/02e1b72a-d68b-42f0-9062-13e62b69e357

Hope this information helps you. Kindly post back with the updated issue for further assistance.
 
Thank you.