Title:
Instagram Graph API: (#3) Application does not have the capability to make this API call on /conversations

Body:
I’m trying to use the Instagram Messaging API via the Graph API, but I’m completely blocked by this error:

{
  "error": {
    "message": "(#3) Application does not have the capability to make this API call.",
    "type": "OAuthException",
    "code": 3
  }
}

This happens when calling:
GET https://graph.facebook.com/v17.0/{ig_user_id}/conversations

What I’ve confirmed:

• The app is in Dev mode (also tried Live).
• The Instagram Business account is connected to a Facebook Page.
• All required permissions (instagram_manage_messages, pages_show_list, etc.) are granted (confirmed via /me/permissions).
• The IG account and Page show up correctly via /me/accounts.
• OAuth flow is completed using the correct scopes.
• Access token is valid.
• I can access /me, /me/accounts, and /1784.../username, etc.

What’s not working:

• The app never appears as "Active" under “Apps and Websites” in the Instagram mobile settings, even after OAuth.
• I've accepted the tester invite, used the full OAuth flow via Instagram mobile browser (sent via DM), and all permissions are granted — but /conversations is still blocked.
• I’ve tested this on multiple accounts, devices, and browsers (including emulators and headless environments).

The Catch-22:

Meta requires /conversations to work in order to submit for App Review — but I can’t get it to work until after review. I’m stuck in a loop: can’t demonstrate the feature without access, and can’t get access without a successful review.

What I’m hoping for:

Has anyone successfully accessed /conversations in Dev mode without passing review?
Is there a missing step to fully activate the app, IG account, or permissions? Any insight would be hugely appreciated.