Graphql subscription in playground during local development throwing "Could not connect to websocket endpoint" in basic nestjs project

This is happening on a simple project during local development, so cloud infrastructure isn't an issue.

This is also happening in the application playground.

My module registration:

 GraphQLModule.forRootAsync<ApolloDriverConfig>({ driver: ApolloDriver, imports: [YeoConfigModule], useFactory: (configService: YeoConfigService<AppConfig>) => { const config: ApolloDriverConfig = { debug: true, subscriptions: { 'graphql-ws': true, }, playground: true, autoSchemaFile: './apps/event-service/schema.gql', sortSchema: true, context: ({ req, res }) => ({ req, res }), }; const origins = configService.get('CORS_ORIGINS')(); config.cors = { origin: origins, credentials: true }; // config.path = '/apis/event-service/graphql'; return config; }, inject: [YeoConfigService], 

My app startup:

async function bootstrap(): Promise<void> { const app = await getApp(); await app.listen(process.env.PORT ?? 3600); } bootstrap(); 

My versions:

 "graphql-ws": "5.11.2", "graphql-redis-subscriptions": "2.5.0" "@apollo/gateway": "2.1.3", "@nestjs/graphql": "10.1.3", "graphql": "16.5.0", 

Result:

{ "error": "Could not connect to websocket endpoint ws://localhost:3600/graphql. Please check if the endpoint url is correct." } 

Any ideas why this isn't working as expected? I've been reading the nestjs docs up at https://docs.nestjs.com/graphql/subscriptions but there's nothing that I can find about extra setup required other than adding

 subscriptions: { 'graphql-ws': true, }, 

when registering the graphql module.