Why does binding a service to a cluster results in service does not support service keys error?

Virtual Private Cloud Classic infrastructure

When you run ibmcloud oc cluster service bind --cluster <cluster_name> --namespace <project> --service <service_instance_name>, you see the following message.

This service doesn't support creation of keys

Some services in IBM Cloud, such as IBM® Key Protect don't support the creation of service credentials, also referred to as service keys. Without the support of service keys, the service can't be bound to a cluster. To find a list of services that support service keys, see Enabling external apps to use IBM Cloud services.

To integrate services that don't support service keys, check if the service provides an API that you can use to access the service directly from your app. For example, if you want to use IBM® Key Protect, see the API reference.