Hello alex
Based on the error message, it says you have already redeemed. If your GitHub account is already linked to another subscription or benefit, it might prevent the redemption of this offer.
I would recommend these steps:
• Log into your Microsoft Founders Hub account.
• Navigate to the Benefits.
• Check if the GitHub Enterprise benefit is marked as redeemed.
You can also proceed to open a support ticket with the Founders Hub support team by following these steps: https://foundershub.startups.microsoft.com/signup?drawer_open=truePlease click on "Support" on this page to submit support ticket.
You can mark it 'Accept Answer' and 'Upvote' if this helped you
Regards,
Abiola