When attempting to create a new Realm using the Red Hat Single Sign-On (RH SSO) API, a 415/HTTP error is returned

Issue

When using the RH SSO API to create a new realm, the following error is returned in the logs:

  [org.keycloak.services.error.KeycloakErrorHandler] (default task-5) Error response 415: javax.ws.rs.NotSupportedException: RESTEASY003065: Cannot consume content type
    at org.jboss.resteasy.resteasy-jaxrs@3.15.3.Final-redhat-00001//org.jboss.resteasy.core.registry.SegmentNode.match(SegmentNode.java:494)
    at org.jboss.resteasy.resteasy-jaxrs@3.15.3.Final-redhat-00001//org.jboss.resteasy.core.registry.SegmentNode.match(SegmentNode.java:175)
    ...
    at org.jboss.xnio@3.8.7.SP1-redhat-00001//org.xnio.XnioWorker$WorkerThreadFactory$1$1.run(XnioWorker.java:1282)
    at java.base/java.lang.Thread.run(Thread.java:829)

The user seems to have the correct permissions.