指定ログイン情報にて自分組織の外部クライアントアプリケーションへの接続エラーシューティング

public with sharing class ContentVersionRenameCallout {

    @future(callout=true)
    public static void renameViaSelfOrgApi(String contentVersionId) {
        Map<String, String> payload = new Map<String, String>{
            'contentVersionId' => contentVersionId
        };

        HttpRequest req = new HttpRequest();
        req.setEndpoint('callout:SalesforceSelf/services/apexrest/ContentVersionRename');
        req.setMethod('POST');
        req.setHeader('Content-Type', 'application/json');
        req.setBody(JSON.serialize(payload));
        req.setTimeout(60000);

        Http http = new Http();
        HttpResponse res = http.send(req);

        if (res.getStatusCode() != 200) {
            // 必要に応じてログ出力や例外化
            System.debug('Callout failed: ' + res.getStatusCode() + ' ' + res.getBody());
        } else {
            System.debug('Callout success: ' + res.getBody());
        }
    }
}

エラー

19:13:41:072 CALLOUT_REQUEST [33]|System.HttpRequest[Endpoint=callout:SalesforceSelf/services/apexrest/ContentVersionRename, Method=POST]

NAMED_CREDENTIAL_RESPONSE NamedCallout[Named Credential Id=null, Named Credential Name=null, Status Code=0, Content-Type=null, Response Size bytes=0, Overall Callout Time ms=0, Connect Time ms=0, Interceptor Time ms=0

19:13:41:401 EXCEPTION_THROWN [33]|System.CalloutException: OAuth トークンを取得できません。

##エラー原因：
トークンエンドポイント URL
誤：https://mydomain--dev01.sandbox.my.force.com/services/oauth2/token
正：https://mydomain--dev01.sandbox.my.salesforce.com/services/oauth2/token