00102: Electronic signature not valid
What it means
SdI code 00102 means the signature on the file does not match its content, so SdI cannot confirm the file is unchanged since it was signed.
The usual cause
Check whether the XML was changed after signing, for example by an editor or a program that reformats it.
How to fix it
Make every change first, then sign the final file and send it without changing it again.
The code as published
Read the official document . Source: Elenco dei controlli effettuati sul file fattura del Sistema di Interscambio, version 2.0, published by Agenzia delle Entrate, fatturapa.gov.it, read on 8 November 2026.
Klarbon explains each code in its own words; the official wording is in the document linked above.