The TSS serial number can be found either via the fiskaly Dashboard in the TSS detail view ("Certificate Serial No."), or in the response of the SIGN DE V2 endpoint retrieveTss (serial_number).
Additionally, the TSS serial number is shown if you use our fiskalcheck App to scan the QR code of a receipt.
For all further data required in order to fulfill the declaration requirement (Mitteilungspflicht) please reach out to your POS provider.