Subscribe a mobile application to an Amazon SNS topic using an Amazon SDK

/**
 * Subscribe an app endpoint to a topic - demonstrates how to initiate a subscription to an Amazon SNS topic
 * with delivery to a mobile app.
 * 
 *  NOTE: You must first create an endpoint by registering an app and device.  
 *     See https://docs.aws.amazon.com/sns/latest/dg/mobile-push-send-devicetoken.html for more information.
 * 
 * <protocol_value> set to "application" provides delivery of JSON-encoded message to an EndpointArn
 *         for a mobile app and device (see https://docs.aws.amazon.com/sns/latest/api/API_Subscribe.html for available protocols).
 * <topic_arn_value> can be obtained from run_list_topics executable and includes the "arn:" prefix.
 * <mobile_endpoint_arn> is the EndpointArn of a mobile app and device.
 */
int main(int argc, char ** argv)
{
  if (argc != 4)
  {
    std::cout << "Usage: subscribe_app <protocol_value/application> <topic_arn_value>"
                 " <mobile_endpoint_arn>" << std::endl;
    return 1;
  }

  Aws::SDKOptions options;
  Aws::InitAPI(options);
  {
    Aws::SNS::SNSClient sns;
    Aws::String protocol = argv[1];
    Aws::String topic_arn = argv[2];
    Aws::String endpoint = argv[3];

    Aws::SNS::Model::SubscribeRequest s_req;
    s_req.SetTopicArn(topic_arn);
    s_req.SetProtocol(protocol);
    s_req.SetEndpoint(endpoint);

    auto s_out = sns.Subscribe(s_req);

    if (s_out.IsSuccess())
    {
      std::cout << "Subscribed successfully " << std::endl;
    }
    else
    {
      std::cout << "Error while subscribing " << s_out.GetError().GetMessage()
        << std::endl;
    }
  }

  Aws::ShutdownAPI(options);
  return 0;
}

Create the client in a separate module and export it.

import  { SNSClient } from "@aws-sdk/client-sns";
// Set the AWS Region.
const REGION = "REGION"; //e.g. "us-east-1"
// Create SNS service object.
const snsClient = new SNSClient({ region: REGION });
export  { snsClient };

Import the SDK and client modules and call the API.

// Import required AWS SDK clients and commands for Node.js
import {SubscribeCommand } from "@aws-sdk/client-sns";
import {snsClient } from "./libs/snsClient.js";

// Set the parameters
const params = {
  Protocol: "application" /* required */,
  TopicArn: "TOPIC_ARN", //TOPIC_ARN
  Endpoint: "MOBILE_ENDPOINT_ARN", // MOBILE_ENDPOINT_ARN
};

const run = async () => {
  try {
    const data = await snsClient.send(new SubscribeCommand(params));
    console.log("Success.",  data);
    return data; // For unit tests.
  } catch (err) {
    console.log("Error", err.stack);
  }
};
run();