clientId

OIDC: REQUIRED. OAuth 2.0 Client Identifier valid at the Authorization Server.

DC API: The client_id parameter MUST be omitted in unsigned requests defined in Appendix A.3.1. The Wallet MUST ignore any client_id parameter that is present in an unsigned request. The client_id parameter MUST be present in signed requests defined in Appendix A.3.2, as it communicates to the wallet which Client Identifier Prefix and Client Identifier to use when authenticating the client through verification of the request signature or retrieving client metadata.

See also clientIdWithoutPrefix and the notes there.