Use Okta core APIs with OIDC application

Our application would like to use Okta OIDC and Core API. Is it possible to do this with just one application? For example can the OIDC application client id / client secret be used to access the Core Okta APIs? Or do we have to have two applications: one OIDC and one API Service Integration? When I attempt to call the oauth2/default/v1/token/token API I get the following error:

“error”: “invalid_client”,
“error_description”: “Only clients with ‘application_type’ of ‘service’ may use the client_credentials ‘grant_type’ with the Org Authorization Server.”