You should check if the secret "vault-n8n-creds-secret" really exists in the Namespace "n8n". (kubectl get secret -n n8n)

Check also events of the SecretProviderClass and watch out for errors. Maybe secret "vault-n8n-creds-secret" cannot be created for some reason.

In addition to that check wether the Role "n8n" has permissions to read Secrets. (kubectl get role -n n8n).