Facebook Graph API - Test User Cannot Access Page Conversations

I'm trying to fetch the conversations from the /conversations endpoint via a page token. Now since the required read_page_mailboxes permission isn't available before review, I'm using the test users for development.

While I'm aware that a test user may not be able to post messages to conversations as specified here http://ift.tt/1woJxTi

I tried to access the pre-created conversations of a page created by a Test User with read_page_mailboxes permission; this however threw an error stating read_mailbox permission was required to access [PAGE-ID]/conversations. So I added the read_mailbox permission to my token process and this time it said

(#298) You must be a developer of the application

Now I tried searching for a way out but as it seems you can not add test users as administrators, so I am unable to test the endpoint.

Finally I decided to use my own real administrator account to test this endpoint but it threw the error

(#210) A page access token is required to request this resource

I debugged the token and it is indeed a page access token, moreover I'm able to use it with the Graph API Explorer (possibly because it has complete permissions.

I'm terribly confused how am I supposed to develop this view and submit the app for review if I cannot even use it.

Any help is appreciated.