I have figured out how to send one basic message to a list of users with sendUsersMessages. However, I can't figure out how to customize the message for each user with substitutions. Also, should I use sendMessages or sendUsersMessages if I am sending unique messages for each user?

The documentation is here, but is hard to understand. All the examples found online seem to just send one push notification.

How can I convert the following to sending different users customized push notifications?

 const gcmRawContent = JSON.stringify({
    data: {
      title,
      message: pushText,
      experienceId,
      channelId,
      body,
    },
  });

  const messageConfiguration = {
    MessageConfiguration: {
      GCMMessage: {
        RawContent: gcmRawContent,
      },
    },
  };

  const sendMessagesParams = {
    ApplicationId,
    SendUsersMessageRequest: {
      Users: { 'userId1': {}, 'userId2': {} },
      ...messageConfiguration,
    },
  };
  const pinpoint = new AWS.Pinpoint();
  await pinpoint.sendUsersMessages(batchSendMessagesParams).promise();