To get approved to "read_page_mailboxes" permission please complete notes in Facebook developer console.

Details to be filled in textarea:

  1. Go to
  2. Login with credentials, email: {your emails}, password: {your password}
  3. Click on one of the project.
  4. Click on “Reengagement”
  5. Click on “Campaigns”
  6. Click on “Add new campaign”
  7. Configure campaign.
After filling all details click Save button.