If it is provided, this id will be used in the SBDH (StandardBusinessDocument/StandardBusinessDocumentHeader/DocumentIdentification/InstanceIdentifier).
If it is not provided, the document identifier in the UBL will be used as default.
If it is provided, this id will be returned in webhooks in a integratorDocumentId field for reference.
If it is not provided, the document identifier in the UBL will be returned in webhooks in a integratorDocumentId field for reference.
In all cases, Digiteal will generate a random UUID for the SBDH (StandardBusinessDocument/StandardBusinessDocumentHeader/DocumentIdentification/InstanceIdentifier).