## Zoho Billing - Product, solutions, integrations, support, and resources Index

Access the complete documentation index at:
https://www.zoho.com/billing/llms.txt

Use this file to discover all available documentation pages before proceeding.

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# What is a chained hash (huella)?

A chained hash or huella is a unique cryptographic code that links each invoice to the previous one in sequence. It ensures that invoices cannot be altered, deleted, or re-numbered without AEAT being able to detect it.

In Zoho Billing, the huella is automatically generated and embedded in the VeriFactu-compliant copy of the invoice when it is sent to AEAT through B2Brouter. You don’t need to add it manually.