App User Collaboration No Longer Grants Access to Shared Folder (404 Not Found)

Our automation has been successfully uploading files to the folder shared by client for several years.

Recently, the integration lost access to the folder.

When authenticating as the App User, the following request returns Not Found:
GET /2.0/folders/ [removed by moderator]

When authenticated as my Box user account (using developer token), I can access the folder without issue
The folder still contains a collaboration for the App User:

{
 "accessible_by": {
 "login": " [removed by moderator] "
 },
 "status": "pending",
 "created_at": "2023-06-26T06:50:34-07:00",
 "modified_at": "2026-06-25T11:56:27-07:00"
}

Notably:

• The collaboration has been in pending status since 2023.
• The integration worked while the collaboration was pending.
• Recreating the collaboration did not resolve the issue.
• Creating new application and sharing the folder did not resolve the issue.
• Not able to accept this collaboration thru API call:

  PUT /2.0/collaborations/{collaboration_id}
  2
  
  3
  {
  4
  "status": "accepted"
  5
  }
  Returns:
  needs_two_factor_authentication
  2
  Two-factor authentication required to accept collaboration or change ownership

  It’s service account so we can not set 2 factor there

Questions:

• Is there any known change affecting App Users and pending collaborations?
• Can an App User be prevented from accessing a folder while an active collaboration record still exists?
• Could a tenant-level security policy (2FA, external collaboration restrictions, Shield policy, etc.) cause this behavior?
• Is there a supported way for an App User to accept a collaboration when Box requires two-factor authentication?
• Could the collaboration have become invalid despite remaining visible through the API?