The Grant Admin Consent page of the Configure Office 365 Mailbox Access Wizard allows you to grant admin consent for the full_access_as_app permission to the Folder Permissions Manager app, which is required the to access mailboxes.
When you are ready, click the Next button.
You will be prompted consent to permissions required by the Folder Permissions Manager app:
Once admin consent has been granted, the wizard moves to the Certificate page.