Excel cannot load Microsoft Store add-ins on Mac or Excel for web

Hello B Robb,

Since the add-in installs and works in Excel for the web, your Microsoft account and Marketplace access appear to be working. The problem is more likely related to Excel for Mac keeping an old sign-in session or another Office app interfering with the add-in service.

I recommend trying these steps:

1. Sign out of both Microsoft accounts in every Office app, then completely close Excel, Word, PowerPoint, Outlook, Teams, and OneNote. Make sure none remain open, restart the Mac, and sign in to Excel using only the account that owns Microsoft 365. A similar Mac case was resolved after the other work account was signed out.
2. Open Excel and select Home > Add-ins > More Add-ins > My Add-ins. If ChatGPT is listed, remove it and add it again.
3. Check System Settings > General > Date & Time, then enable automatic date and time and confirm the correct time zone.

As an additional test, you could create a new standard macOS user account, sign in to that account, then open Excel and sign in only with the Microsoft account that owns the Microsoft 365 subscription. If the add-ins work there, the issue is likely limited to settings or sign-in data in the original Mac profile. For detailed steps, see: Add a user or group on Mac.

Disclaimer: While the article above is not a Microsoft website, it is the official site of Apple.

Please let me know how it goes after trying these steps, and I'll be glad to continue looking into it with you.