If, for any reason, you cannot provide proof of funds covering your stay in Austria, you will have to get your Austrian host to sign a declaration of liability for you.
This declaration of liability is an Electronic letter of guarantee referred to as Elektronische Verpflichtungserklärung or Generalverpflichtungserklärung (EVE or GVE).
When an application is made for an EVE with the concerned local authority, the authority will conduct a verification of the identity of the host and review the financial status of the Austrian host. Once the verification is completed and the declaration of liability signed, an 8-digit ID-number is issued to the host. It is this ID-number that will be required by the Austrian Consulate or Embassy at the time of applying for the visa.