Command not found: sst | There was an error synthesizing your app

I am trying to provision aws ECS using aws cdk with sst in seed. And I got this issue saying command not found: sst

The logs says this:

$ cd /tmp/seed/source
INFO: before_build hook not found. You can define it in your build spec.
INFO: Learn more about adding a build spec - seed.run/docs/adding-a-build-spec

$ cd /tmp/seed/source/backend/apollo-sst-test

$ npx sst build --stage devops --region ap-southeast-2 --verbose

npx: installed 1 in 1.171s
command not found: sst

ERROR: There was an error synthesizing your app.
INFO: Build completed in 2m 49s. Used 0 build minutes.

Mystack.js code is

import * as sst from "@serverless-stack/resources";
import * as ec2 from "@aws-cdk/aws-ec2";
import * as ecs from "@aws-cdk/aws-ecs";
import * as ecs_patterns from "@aws-cdk/aws-ecs-patterns";
import * as ecr from "@aws-cdk/aws-ecr";
import { DockerImageAsset } from '@aws-cdk/aws-ecr-assets';
import path from "path";
import process from  "process";

export default class MyStack extends sst.Stack {
  constructor(scope, id, props) {
    super(scope, id, props);

    // Define your stack
    const vpc = new ec2.Vpc(this, "myvpc", {
      maxAzs: 2 // Default is all AZs in region
    });

    const cluster = new ecs.Cluster(this, "mycluster", {
      vpc: vpc
    });

    //#endregionconst repo = new ecs.RepositoryImage("apollo-server");
    
    // const asset = new DockerImageAsset(this, 'MyBuildImage', {
    //   directory: path.join(__dirname, '../../apollo')
    // });
    const repo = ecr.Repository.fromRepositoryName(this, "apollo-server-2", "apollo-server-2");
    
    // Create a load-balanced Fargate service and make it public
    const loadBalancedFargateService = new ecs_patterns.ApplicationLoadBalancedFargateService(this, "myfargate-alb", {
      cluster: cluster, // Required
      cpu: 256, // Default is 256
      desiredCount: 1, // Default is 
      taskImageOptions: { image: ecs.ContainerImage.fromEcrRepository(repo)},
      memoryLimitMiB: 512, // Default is 512
      publicLoadBalancer: true,// Default is false
      environment: {
        stage: process.env.stage,
        cognitoConfig: `https://build-config-bucket-${process.env.stage}.s3-ap-southeast-2.amazonaws.com/cognito-config.json`,
	      databaseConfig: `https://build-config-bucket-${process.env.stage}.s3-ap-southeast-2.amazonaws.com/database-config.json`,
	      erwteConfig: `https://build-config-bucket-${process.env.stage}.s3-ap-southeast-2.amazonaws.com/erwte-config.json`

      }
    });
    loadBalancedFargateService.targetGroup.configureHealthCheck({
      path: "/.well-known/apollo/server-health",
    });
    

  }
}

Hmm that seems weird. Can you send us an email to contact@seed.run with a link to this build ?