The electronic signature is gray, because it can't be signed for network reasons, and the verification system of the tax bureau is faulty. When the invoice is uploaded on the network, the digital tax certificate will be invalid during the process of adding digital signature to the electronic invoice, and the verification system of the tax bureau will also fail.

These are caused by non-human factors, which are rare, but they are inevitable at present. Failed invoices must be voided and reissued, and cross-month invoices need to be reissued by the tax bureau stub.