When troubleshooting Trello attachment and file sharing issues, the most common problems stem from file size limitations, browser compatibility, integration errors, and API changes. Users frequently encounter difficulties uploading attachments due to exceeding Trello’s file size limits (10 MB for free accounts, 250 MB for premium) or unstable network connections ^[6]. Browser-related issues, such as outdated versions, conflicting extensions, or disabled cookies, can also prevent attachments from uploading or downloading properly ^[2]. Integration tools like Zapier or Make (formerly Integromat) may fail to process files correctly if the wrong data fields are mapped or if API endpoints are misconfigured ^[3]. Additionally, recent changes to Trello’s API require updated authentication methods for downloading attachments, which can break existing workflows ^[8].

Key findings to address first:

• File size limits: Free accounts are capped at 10 MB per attachment, while premium accounts support up to 250 MB ^[6].
• Browser issues: Outdated browsers, disabled cookies, or conflicting extensions often block uploads/downloads ^[2].
• Integration errors: Automations via Zapier or Make may fail if file data isn’t properly mapped or if API endpoints are outdated ^[3].
• Missing file extensions: Downloaded attachments may lack extensions, requiring manual renaming ^[5].

Troubleshooting Trello Attachment and File Sharing Issues

File Upload and Size Limitations

Trello enforces strict file size limits that vary by account type, which is a primary cause of upload failures. Free accounts are restricted to 10 MB per attachment, while premium users can upload files up to 250 MB ^[6]. Exceeding these limits results in failed uploads, often without clear error messages. Users should first verify the file size and compress or split large files if necessary. Network instability can also disrupt uploads, so checking connectivity and retrying on a stable network is recommended ^[6].

For persistent upload issues, clearing the browser cache or switching to a supported browser (Chrome, Firefox, Edge, or Safari) may resolve hidden conflicts ^[2]. Trello’s support documentation emphasizes that:

• Free accounts have a 10 MB per file limit, while premium accounts support 250 MB ^[6].
• Unsupported file types (e.g., certain audio or video formats) may fail to upload even if under the size limit ^[3].
• Compressing files or using cloud storage links (Google Drive, Dropbox) can bypass size restrictions ^[6].
• Network timeouts or firewalls may block uploads, requiring a switch to a different network or disabling VPNs ^[2].

If uploads still fail, users should test with smaller files or different file types to isolate the issue. For example, a user in the Zapier Community resolved a .wav file upload error by ensuring the automation targeted the correct file object and used looping actions for multiple attachments ^[3].

Browser and Extension Conflicts

Browser-related issues are another major cause of attachment problems in Trello. Outdated browser versions, disabled cookies, or conflicting extensions (e.g., ad blockers, privacy tools) can prevent files from uploading or downloading correctly ^[2]. Trello’s support team recommends a systematic approach to diagnose these issues:

• Update the browser to the latest version, as Trello optimizes performance for recent releases of Chrome, Firefox, Edge, and Safari ^[2].
• Disable all extensions temporarily, then re-enable them one by one to identify conflicts. Extensions like uBlock Origin or Privacy Badger may interfere with file operations ^[2].
• Use incognito/private mode to rule out cached data or extension interference. If attachments work in incognito, the issue likely stems from a regular browser setting or extension ^[2].
• Enable cookies for Trello’s domain, as blocked cookies can disrupt file handling. Instructions for enabling cookies vary by browser (e.g., Chrome: Settings > Privacy > Cookies) ^[2].
• Clear cache and cookies if attachments fail to load or download. Corrupted cached data can cause Trello to behave unpredictably ^[2].

A Reddit user reported that downloaded attachments suddenly lacked file extensions, requiring manual renaming (e.g., adding .pdf or .jpg) ^[5]. While this isn’t a browser issue per se, it highlights how Trello’s backend changes can affect file handling. Users experiencing this should check if the issue persists across browsers or devices to determine if it’s a widespread Trello update or localized problem.

For advanced troubleshooting, Trello suggests checking the browser’s console logs (F12 > Console) for errors during uploads/downloads. Errors like 403 Forbidden or CORS issues may indicate permission problems or API restrictions ^[2].

Integration and API Issues

Third-party integrations (Zapier, Make, n8n) and API changes frequently cause file-sharing failures in Trello. Automations may break if:

• The wrong data field is mapped (e.g., mapping a file name instead of binary data) ^[4].
• The API endpoint is outdated, as Trello has updated its attachment retrieval method to require header-based authentication ^[8].
• File permissions are misconfigured, leading to unauthorized errors (e.g., Google Drive integrations) ^[3].

In the Make Community, users resolved attachment issues by:

1. Using the HTTP "Get File" module to fetch actual file data from sources like Airtable before attaching to Trello ^[4].
2. Ensuring the Trello "Add an Attachment" module receives binary data, not just filenames or links ^[4].
3. Switching to Trello’s new attachment API endpoint, which requires credentials in the header, not query parameters ^[8].

For Zapier users, a common fix involves:

• Checking Zap history to identify where the automation fails (e.g., during file upload or link generation) ^[3].
• Using looping actions to handle multiple attachments sequentially, as parallel processing may cause conflicts ^[3].
• Verifying Google Drive permissions when generating shareable links, as insufficient scopes can trigger unauthorized errors ^[3].

If attachments download as corrupted files or lack extensions, users in the n8n and Make communities recommend:

• Using the HTTP "Get a File" module instead of Trello’s native "Get an Attachment" module ^[9].
• Manually adding file extensions (e.g., .pdf) to downloaded files if Trello’s API omits them ^[5].