You can set a client which is no longer used to the state "DEREGISTERED"
.
This is done via the SIGN DE API V2 endpoint updateClient.
Please note, before changing the state of a client, an admin authentication must be processed.
A client with a TSS in the state DISABLED
can no longer be updated.
However, a client that is connected to a TSS in the state DISABLED
can no longer be used and will not be invoiced.
Relevant article:
SIGN DE - When exactly do I need the authenticate admin call?