API-uploaded documents not accessible by other users (default document library)

We're building an integration between a third-party document signing service and SuperOffice using n8n. When a document is signed, a webhook triggers our flow which:

1. Updates the Sale status to Sold
2. Creates a Document entity (POST /api/v1/Document)
3. Downloads the signed PDF
4. Uploads PDF content (POST /api/v1/Agents/Document/SetDocumentStreamFromId)

Everything works - the document is created, PDF is uploaded, I can open it. But other users cannot open the PDF, even though:

• VisibleFor is set to "All"
• Associate is set to the Sale owner
• Both users have full admin permissions (User level 0, all data rights set to Delete)
• We use the default SuperOffice document library (not SharePoint)

API calls are authenticated with my OAuth credentials (Authorization Code flow). The document shows CreatedBy = me, even though Associate = other user.

We verified the PDF is actually stored - GET /api/v1/Document/{id}/content returns the full PDF data.

Is this a known limitation? Do we need a system user or separate integration account for document uploads to be accessible by everyone?