When adding an external TSS to your Establishment via the endpoint Create or update an external TSS, you need to use the required field bsi_id.
The BSI ID corresponds to the ID of the certificate issued by the German Federal Office for Information Security (BSI - Bundesamt für Sicherheit in der Informationstechnik).
The certificate ID of a fiskaly TSS (as well as the ID of other certified Technical Security Systems) is published on the official page of the German Federal Office for Information Security.
Example:
Name: fiskaly sign Cloud-TSE
Certificate ID: BSI-K-TR-0717-2025
In this case, the correct value for the field bsi_id would be 0717-2025.