When Yettel's service center is not authorized to perform warranty or post-warranty support for goods purchased from corporate clients (or leased, as the case may be) in order to be able to perform the obligation to provide free repair or replacement, or to fulfil a post-warranty repair request, we use the services of authorized external service centers. In accordance with manufacturer’s authorization requirements, in order to be able to perform warranty repairs or replacement of goods, the external service centers require Yettel to provide proof of purchase (e.g. copies of invoices, warranty cards, etc.). This is also the case where a corporate client's claim is unreasonable, but the client wants a post-warranty repair.