invalid_grant when using Java SDK

Hi all - I'm working on my initial box integration using a service account setup for App+Enterprise access. I'm receiving an invalid_grant - Grant credentials are invalid in response to this block of code. My clientId is 9fxqtste70ak8rcrf726p90aepxira09.

BoxCCGAPIConnection boxApi = BoxCCGAPIConnection.applicationServiceAccountConnection(
    clientId, secret, enterpriseId
);
BoxFolder folder = BoxFolder.getRootFolder(boxApi);
for (BoxItem.Info itemInfo : folder) {
  if (itemInfo instanceof BoxFile.Info) {
    BoxFile.Info fileInfo = (BoxFile.Info) itemInfo;
    log.info("fileInfo = " + fileInfo.getName());
    // Do something with the file.
  } else if (itemInfo instanceof BoxFolder.Info) {
    BoxFolder.Info folderInfo = (BoxFolder.Info) itemInfo;
    log.info("folderInfo = " + folderInfo.getName());
    // Do something with the folder.
  }
}