Oauth2-error upon starting REST-driver

I'm in the process of setting up a REST-driver using OAuth-authentication for the first time.

It seems the driver is trying to get a token upon driver start, but it fails, seemingly becuase the token endpoint is expecting a request formatted as JSON and I suspect the driver is sending it as XML.

Here's the trace, that also shows the subscriber config. Trace level is 10, but I don't see the request or response sent to/received from the token endpoint:

<nds dtdversion="4.0" ndsversion="8.x">
<source>
<product edition="Advanced" version="4.7.0.0">DirXML</product>
<contact>NetIQ Corporation</contact>
</source>
<input>
<init-params src-dn="\HRG\system\driverset1\MySite">
<driver-filter>
<allow-class class-name="User">
<allow-attr attr-name="userName"/>
<allow-attr attr-name="name.formatted"/>
<allow-attr attr-name="active"/>
<allow-attr attr-name="name.givenName"/>
<allow-attr attr-name="emails"/>
<allow-attr attr-name="addresses"/>
<allow-attr attr-name="phoneNumbers"/>
<allow-attr attr-name="name.familyName"/>
<allow-attr attr-name="title"/>
</allow-class>
</driver-filter>
<subscriber-options>
<subAuthMethod display-name="Authentication Method">OAuth</subAuthMethod>
<subAuthBasicID display-name="Authentication ID"></subAuthBasicID>
<subAuthBasicPwd display-name="Authentication Password" is-sensitive="true" type="password-ref"/>
<bearerToken display-name="Bearer Token">hide</bearerToken>
<bearerTokenID display-name="Bearer Token ID"></bearerTokenID>
<subOAuthURL display-name="Access Token URL">https://mysite.com/configapi/v2/oauth/token</subOAuthURL>
<subOAuthID display-name="User Name"></subOAuthID>
<subOAuthPwd display-name="User Password" is-sensitive="true" type="password-ref"/>
<query-name display-name="Query Name">grant_type</query-name>
<query-value display-name="Query Value">client_credentials</query-value>
<query-name display-name="Query Name">client_id</query-name>
<query-value display-name="Query Value">admin</query-value>
<query-name display-name="Query Name">client_secret</query-name>
<query-value display-name="Query Value">*****************************************</query-value>
<query-name display-name="Query Name">scope</query-name>
<query-value display-name="Query Value">mysite.com</query-value>
<header-name display-name="Header Name">content-type</header-name>
<header-value display-name="Header Value">application/xml</header-value>
<subTrustStoreFile display-name="Truststore file">E:\NetIQ\IdentityManager\RESTDriversKeystore.jks</subTrustStoreFile>
<mutualFields display-name="Set mutual authentication parameters">hide</mutualFields>
<subKeystoreFile display-name="Keystore file"></subKeystoreFile>
<subKeystorePassword display-name="Keystore password" is-sensitive="true" type="password-ref"/>
<connTimeOut display-name="Http Connection Timeout">1</connTimeOut>
<proxy display-name="Proxy host and port"></proxy>
<proxyFields display-name="Set proxy authentication parameters">hide</proxyFields>
<proxyUserName display-name="User name"></proxyUserName>
<proxyPassword display-name="Password" is-sensitive="true" type="password-ref"/>
<subHttpErrorsToRetry display-name="HTTP errors to retry">307 408 503 504</subHttpErrorsToRetry>
<subHttpRESTBASEURL display-name="Base URL for REST Resources">https://mysite.com/configapi/v2/scim/</subHttpRESTBASEURL>
<resrc-schemaName display-name="Schema name">User</resrc-schemaName>
<resrc-operationMode display-name="Configure Handlers">CUSTOM</resrc-operationMode>
<resrc-handlerConf display-name="Rest Handler Details">users/#0#1# users/&lt;association>&lt;filter>#2#0# users/&lt;association>/#1#3# users/&lt;association>#3#1#</resrc-handlerConf>
</subscriber-options>
</init-params>
</input>
</nds>
[10/07/19 15:13:39.220]:BP ST:MySite: RESTSubscriptionShim.init()
[10/07/19 15:13:39.220]:BP ST:MySite: Connecting to REST service via OAuth2
[10/07/19 15:13:39.957]:BP ST:SubscriptionShim.init() returned:
[10/07/19 15:13:39.957]:BP ST:
<nds dtdversion="3.5" ndsversion="8.x">
<source>
<product build="20180222_0635" instance="MySite" version="1.0.0.2">Identity Manager REST Driver</product>
<contact>NetIQ Corporation.</contact>
</source>
<output>
<status level="fatal" type="app-authentication">org.codehaus.jettison.json.JSONException: A JSONObject text must begin with '{' at character 1 of &lt;html>&lt;head>&lt;meta http-equiv="Content-Type" content="text/html;charset=utf-8"/>&lt;title>Error 415 Unsupported Media Type&lt;/title>&lt;/head>&lt;body>&lt;h2>HTTP ERROR 415&lt;/h2>&lt;p>Problem accessing /configapi/v2/oauth/token. Reason:&lt;pre> Unsupported Media Type&lt;/pre>&lt;/p>&lt;hr>&lt;a href="http://eclipse.org/jetty">Powered by Jetty:// 9.4.12.v20180830&lt;/a>&lt;hr/>&lt;/body>&lt;/html></status>
</output>
</nds>