Excel add-ins will not download or install

Question

Hi -- I am unable to download and install add-ins in my Excel. I have been through two full troubleshooting sessions with Microsoft support where they went through their full list of things to try. They eventually gave up and sent me here. When I attempt to download any add-ins through excel I get an "error loading add-ins" message. When I go directly to the add-in developer's site and attempt to download it directly, I get a "502 Bad Gateway" error. Among other things, I have reinstalled windows 11 a few times now and that hasn't fixed it. Any help appreciated. Thanks.

Answer 1

My Excel adds-in won't load, either.

Since yesterday, I have had the exact same experience as the OP and @donutvector. Spent hours with tech support, but it's the same on both my machines.

If you are getting "We can't load this add-in because we couldn't connect to the catalog" and the See Details link sends you to a 502 Bad Gateway page, I can save you hours of useless tech support that attempts to find the problem with your setup: it's a Microsoft side problem.

Answer 2

Dear @AJS,   

I’ve submitted this feedback directly to Microsoft through the official Feedback Portal so the product team can review it. You can find the feedback here: Excel Add-ins Fail to Download or Install (Likely AppSource and Office Store Service Issue) · Community 

I strongly encourage you to upvote the idea and add a comment with your scenario. The more votes and real‑world examples it receives, the higher the visibility it gets with the product team. 

When I come across other users reporting the same or similar issue, I’ll direct them to this feedback so they can upvote it as well and help consolidate impact in one place. 

Additionally, other users have raised similar concerns and may not be aware of where to share their feedback. Highlighting this information can make it more visible to others in the community who may be facing the same issue, making it easier for them to find guidance and contribute their feedback as well.   

Thanks again for taking the time to report this and for helping bring more attention to the issue. 

Answer 3

I'm seeing the same 502 Bad Gateway on pages.store.office.com/addininstaller.aspx when trying to install any add-in via the Web. Also getting "Error loading add-ins" when attempting to install any add-in directly from Excel desktop. I have reproduced the error on multiple PCs. Also, there have been multiple reports on Microsoft Q&A over last 48 hours with exact same symptoms. This is almost certainly a Microsoft-side problem.

Answer 4

Dear @AJS, 

Thank you for posting your question in the Microsoft Q&A forum.   

I understand how inconvenient it must be to repeatedly troubleshoot this issue. 

Based on what you described, the error “Error loading add-ins” in Excel can occur for several reasons, including connectivity issues, policy restrictions, WebView2 runtime problems, cache corruption, or conflicts with other add-ins.  

To better understand your environment and provide accurate guidance, it would be very helpful if you could share a bit more information: 

1/ When you mentioned that you had two full troubleshooting sessions, did you contact Microsoft Support through the Contact Us page for Home or Business Support, or was this support accessed through the Microsoft 365 admin center? 

2/ Could you provide a summary of the troubleshooting steps that were already attempted? 

3/ Which version of Excel are you installing the add-in on Windows, macOS, or the web version? 

Since you did not specify whether you are using a work, school, or personal account, and whether you are an IT administrator or an end‑user, I would like to offer several options you can try to help isolate the issue: 

• Make sure both your operating system, Excel and browser are fully updated.     
• Verify date and time accuracy: Close all Office applications, check that Windows date, time, and time zone are correct, then reopen Excel and try installing the add-in again. Incorrect time settings can cause manifest validation to fail. 

Note: If you have already tried any of the steps below, please let me know. 

Option 1: Connectivity and identity checks inside Excel 

Step 1: Sign out of Excel by going to File > Account > Sign out. 

Step 2: Close Excel. 

Step 3: Reopen Excel and sign in again with your Microsoft 365 account. 

Step 4: Open a private or incognito browser and go to office.com and sign in your account > Apps > Excel and check whether Insert > Add-ins loads successfully. 

If the add-in loads correctly in the web version but not on the desktop version, this usually indicates a local runtime or configuration issue on the machine. 

Option 2: Start Excel in safe mode to identify conflicts 

Step 1: Press Windows Key + R. 

Step 2: Type: excel /safe. 

Step 3: Check whether the add-in section loads successfully. 

Step 4: If it loads successfully, reopen your normal Excel application and go to File > Options > Add-ins. 

Step 5: Choose Manage: COM Add-ins > Go. 

Step 6: Disable other add-ins one by one to identify which one is causing the conflict. 

Option 3: Clear the Office add‑in cache (Windows) 

Step 1: Close every Office application. 

Step 2: Open File Explorer. 

Step 3: Enter the following path in the address bar: %localappdata%\Microsoft\Office\16.0\Wef 

Step 4: Delete everything inside the WEF folder, but do not remove the folder itself. 

Step 5: Open Excel again and try using Get Add-ins. 

Option 4: Repair office 

This article provides further guidance on the topic: Repair an Office application - Microsoft Support  

Option 5: Reinstall office 

Please uninstall all office apps. Then sign in at office.com > Apps > Install apps > Microsoft 365 apps > Apps & devices > Install Office.   

Option 6: Review policies that may block add‑ins 

Note: These steps need to be performed by your IT administrator. If you are an end user, please contact your IT team for assistance. 

1/ Tenant-level policies 

Step 1: Open the Microsoft 365 admin center. 

Step 2: Navigate to Settings > Org settings > User owned apps and services. 

Step 3: Make sure “Let users access the Office Store” is enabled. 

2/ Local group policy 

Check whether the Local Group Policy setting “Block all unmanaged add-ins" is enabled and if it is, please disable it. 

3/ Ensure Microsoft 365 endpoints are reachable 

If your work network uses strict firewalls or proxies, Microsoft 365 endpoints such as office.com, appsource.microsoft.com and related CDNs must be allowed. Ensure HTTPS traffic on ports 80 and 443 is not being filtered or blocked. Bypassing SSL inspection for Microsoft Optimize and Allow categories may also help prevent disruptions. 

4/ Contact Microsoft Support via Microsoft 365 admin center 

If the issue persists after these checks, I sincerely recommend reaching out to your IT administrator to create a support ticket via Microsoft 365 Admin Center > Support > Help & Support for further investigation. 

A technical support engineer can perform a remote session to investigate the situation, verify the backend configurations, and run any necessary synchronization tools to resolve the problem. If the issue requires further attention, they can escalate it to a specialized team for deeper analysis.     

• Regarding the vendor site showing “502 Bad Gateway”: 

Since the developer’s website also returns a 502 error, please try the following: 

Step 1: Attempt to download the add‑in using a different browser. 

Step 2: Try a different network such as a mobile hotspot. 

Step 3: Retry after some time. 

Optional: You may also ask a colleague to try adding the add‑in or accessing the developer’s website to help confirm whether the issue is widespread. 

If the 502 error continues across multiple networks or devices, it likely indicates a temporary outage or configuration error on the vendor’s server.  

Additional information is available in the following resources: 
Troubleshoot user errors with Office Add-ins - Office Add-ins | Microsoft Learn 

No Add-ins Loaded Because of Group Policy Settings - Microsoft 365 Apps | Microsoft Learn 

Clear the Office cache - Office Add-ins | Microsoft Learn 

Manage add-ins in the admin center - Microsoft 365 admin | Microsoft Learn 

Microsoft 365 URLs and IP address ranges - Microsoft 365 Enterprise | Microsoft Learn 

As community moderators, we kindly ask for your understanding that our access to internal development details is limited. Our primary role is to guide users toward the appropriate resources and support channels. While we may not have visibility into performing deeper backend analysis, we’ll continue doing our best to support you within the scope of our responsibilities.  

I hope this information is helpful. If you have any questions or need further support, please don’t hesitate to reach out at any time. 

Thank you for your patience and understanding. 

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Answer 5

To troubleshoot the issue with downloading and installing Excel add-ins, you can follow these steps:

1. Check the Time and Date: Ensure that the time and date on your computer are set correctly, as incorrect settings can cause issues with verifying the add-in's manifest.
2. Verify the Manifest: If you have access to the add-in's manifest, verify that it is valid. You can find guidance on how to validate an Office Add-in's manifest in the Microsoft documentation.
3. Close and Restart Office: Sometimes, simply closing Excel and reopening it can resolve temporary issues.
4. Reinstall the Add-in: If the add-in package was tampered with, you may need to download it again from a reliable source and try to install it once more.
5. Check Firewall Settings: If you receive an error indicating that the catalog could not be reached, verify your firewall settings to ensure that they are not blocking access to the Microsoft Marketplace.
6. Update Office: Make sure that you have the latest updates for Office installed. You can update Office through the Windows Installer if necessary.
7. Registry Check: If you continue to face issues, there may be incorrect information in the Windows registry. You can check the registry settings related to Office add-ins, but be cautious as modifying the registry can lead to serious issues if done incorrectly.

If these steps do not resolve the problem, consider reaching out to the add-in developer for further assistance or checking for any known issues with the add-in itself.

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References:

• Troubleshoot user errors with Office Add-ins
• Error: "We can't start this app" when you install an Office add-in