This is a known bug in saas-19.3 where attachment.raw returns a LocalBinaryFile object (not raw bytes), causing urllib3 to fail because it cannot determine the content length.

**Immediate Workaround (no code needed):**

Use a URL-based document header instead of a file upload:

• In your WhatsApp Template, set Header Type = Document

Enter a public URL to your document instead of uploading a file

• This bypasses the _upload_demo_document method entirely

**For Odoo Online (saas-19.3 Enterprise):**

Since you cannot modify server files directly:

1. Submit a bug report to Odoo Support through your Enterprise subscription portal - this is a server-side bug they should hotfix
2. 2. Use the URL workaround above in the meantime
3. 3. Switch to Text header type for your templates until the patch is deployed

**Technical Root Cause:**

The bug is in whatsapp/tools/whatsapp_api.py where data=attachment.raw is passed directly. The fix would be reading the bytes first with attachment.raw.read() but on Odoo Online you cannot apply this patch yourself. This is Odoo's bug to fix.

Hope this helps - please upvote so Odoo prioritizes the fix!