From the OAuth2 RFC7662, the token_type for introspect in Section 2.2 should also follow is follow Section 7.1 of RFC6749. https://tools.ietf.org/html/rfc6749#section-7.1. The token_type should be Bearer (if this indeed is a Bearer token).
Currently this is seen:
An example of token_type can be seen for /oauth2/introspect in OPENAM-8980.