Batch issuance appears broken

[Didr]

After adding the following configuration:

apigw:
      issuer_metadata:
        batch_credential_issuance:
          batch_size: 2

I then receive the following error when trying to issue a credential:

ERROR    apigw.apiv1    proofs verification failed    {"error": "invalid_proof: token signature is invalid: crypto/ecdsa: verification error"}                    
ERROR    apigw.httpserver    VCICredential error    {"error": "invalid_proof: token signature is invalid: crypto/ecdsa: verification error"}

Possibly related to #346 not being completed?