ChatGPT File Upload Failed: Network Checks

A successful prompt does not prove ChatGPT can upload files. Uploads use a different path, a different domain and different limits from ordinary chat, so check those before blaming the file.

Symptoms

• Text prompts work, but attaching a file shows "Upload failed", "Unable to upload" or a spinner that never finishes.
• The upload works on a phone using mobile data, but fails on the office Wi-Fi or over the VPN.
• Small text files upload, but a PDF, spreadsheet or image fails.
• The file uploads, but ChatGPT then says it cannot read or open it.
• Downloading a file that ChatGPT generated fails, or the link opens a blank page.

Note which of these you are seeing. They point to different causes.

Likely causes, most common first

1. A network control blocks the upload domain. ChatGPT sends and serves file content through the oaiusercontent.com domain family, not through chatgpt.com alone. A firewall, DNS filter or web proxy that allows chatgpt.com but not *.oaiusercontent.com will pass chat and fail uploads. The same rule usually breaks downloads of generated files.
2. TLS inspection or a data loss prevention rule interferes with the transfer. Some secure web gateways inspect uploads and drop or rewrite large multipart requests. Chat text passes because it is small. This often looks like a timeout rather than a clear error.
3. The file breaks a documented limit. OpenAI publishes limits on file size, number of files per conversation and total storage per user. These change, so check the current file uploads page rather than assuming last year's figure.
4. The file type is not supported for that feature. A file type that works with data analysis may not work in a project, a custom GPT or a connector. Password-protected PDFs and scanned images with no text layer are common failures.
5. Workspace policy. In ChatGPT Team and Enterprise, administrators can control some features at workspace level. If uploads fail for everyone on a business plan, check the workspace settings before checking the network.
6. Browser state. An old service worker, an extension that blocks scripts or a blocked third-party cookie can stop the upload request from starting at all.

Step-by-step fix

1. Confirm the platform is up. Check the OpenAI status page for an incident affecting uploads or attachments.
2. Try the same file on a phone hotspot with the VPN off. If it works there and fails in the office, the cause is the office network. Stop here and go to the IT checks below.
3. Try a tiny plain-text file. If that works and the real file fails, the problem is the file: size, type, protection or a corrupt document.
4. Open a private browsing window with extensions disabled and try again. If it works, clear site data for chatgpt.com in the normal profile or remove the extension that interferes.
5. Try the desktop app or a different browser. If the app works and the browser does not, the fault is in the browser profile.
6. Ask a colleague on the same plan to try the same file. If it fails only for you, check your storage usage and remove old files from projects you no longer use.
7. Record the exact error text, the time, the file type and size, and whether you were on the VPN. That is what IT or OpenAI support will ask for.

What IT or the administrator should check

• Allow the full set of domains OpenAI lists for ChatGPT, including *.oaiusercontent.com and *.oaistatic.com, in DNS filtering, the web proxy and the firewall. Allowing chatgpt.com on its own is not enough.
• Look at the proxy log at the time of the failed upload. A blocked category, a size limit on POST requests or a "content inspection failed" entry is the answer.
• If you run TLS inspection, consider excluding the upload domain from inspection, or set a documented exception for the AI tools your business has approved. Keep the exception narrow.
• If Microsoft Defender for Endpoint web content filtering is in use, confirm that the generative AI category or the specific domains are permitted for the right device group. Our note on web content filtering in Defender for Business covers where those settings live.
• For Team and Enterprise, check the workspace admin settings for any feature restriction that touches files, and confirm the user is in the right group.
• Check any endpoint DLP policy that blocks uploads of labelled or classified documents to unapproved cloud apps. That may be working exactly as intended.

Whatever you change, write it down with the date and the reason. A silent allow rule for a whole domain family is the kind of thing that fails a Cyber Essentials Plus conversation later.

When to escalate to OpenAI

Raise a support case when uploads fail on a clean network, with a small supported file, in a private window and after the status page shows no incident. Include the error text, the timestamp, the browser and version, your plan and whether the failure is one user or the whole workspace. Team and Enterprise administrators should raise the case from the admin account so support can see the workspace.

If the failure is only on your network, OpenAI cannot fix it. The domain list on their network recommendations page is the reference to hand to whoever manages your firewall.

Source basis

• OpenAI status page
• Microsoft: web content filtering in Defender for Endpoint
• Cloudflare: Gateway HTTP policies