Palo Alto Firewall blocks downloading files from DropBox with there errors: something went wrong or There was an error downloading your file

Problem: We have PA firewall 440. We have added dropbox.com to OBJECTS>Custom Objects>URL Category and can login dropbox. However, can’t download files with these errors: .pdf files are supported but something went wrong or There was an error downloading your file.

Troubleshooting:

1. Login PA firewall.
2. Go to MONITOR>Logs>URL Filtering.
3. Add the source IP address, for our example ( addr.src in 192.168.10.10 ).
4. We can see ACTION block-url and URL for example previews.dropbox.com.

5. After we add previews.dropbox.com/, consent.dropbox.com/, we can download files from Dropbox.

Note: Dropbox uses a mix of random URL and includes across multiple domains.  Here are some exalples:

dropbox.com/
*.dropbox.com/
dropboxapi.com/
*.dropboxapi.com/
getdropbox.com/
*.getdropbox.com/
dropboxstatic.com/
*.dropboxstatic.com/
dropboxcaptcha.com/
*.dropboxcaptcha.com/

So, the best resolution is configuring a security rule. Please refer to this post:

Create a Policy to allow accessing Dropbox on PA Firewall