This carries a free-text error message describing the specific fault condition detected on the decap label/tunnel referenced by the notification, giving a plain-language reason rather than just a numeric fault code. This is the field admins actually read to understand why something failed, as opposed to correlating indices and states across several other objects. For example, the message might read something like 'Label not found in forwarding table' or 'LSP down,' immediately telling the engineer the nature of the problem without further digging.