minor tweaks to language

openid-4-verifiable-credential-issuance-1_0.md

@@ -774,12 +774,10 @@ Content-Length: 0
 
 The Credential Issuer provides a nonce value in the HTTP response with a 2xx status code and the following parameters included as top-level members in the message body of the HTTP response using the application/json media type:
 
-* `c_nonce`: REQUIRED. String containing a nonce to be used when creating a proof of possession of the key proof (see (#credential-request)).
+* `c_nonce`: REQUIRED. String containing a nonce to be used when creating a proof of possession of the key proof (see (#credential-request)). This value MUST be unpredictable and unique for every response returned from the nonce endpoint.
 
 Due to the temporal and contextually sensitive nature of the `c_nonce` value, the Credential Issuer MUST make the response uncacheable by adding a `Cache-Control` header field including the value `no-store`.
 
-A wallet SHOULD assume that the returned `c_nonce` value remains valid and continue using it in credential requests (see [#credential-request]) until the credential endpoint returns an `invalid_nonce` error response.
-
 Below is a non-normative example of a Nonce Response:
 
 ```