AWS Appsync enhanced subscription filtering not working

Question

AWS enhanced subscription filtering feature documentation recommends to add the following response mapping template:

## Response Mapping Template - onSpecialTicketCreated subscription

$extensions.setSubscriptionFilter($util.transform.toSubscriptionFilter($util.parseJson($ctx.args.filter)))

$util.toJson($context.result)

When using a simple request mapping template the subscription will not return any data:

{
    "version": "2017-02-28"
}

Answer 1

The documentation does not mention the following (got it though one month of back and forth with support):

In the request template the payload must be set:

{
    "version": "2017-02-28",
    "payload": {}
}

If you have fieldLevel resolver note that for some reason they are executed when the subscription is set up and a payload is set. To accommodate this make sure they handle that i.e. event.source.id is not defined. For them to work pass the args as payload:

{
    "version": "2017-02-28",
    "payload": $util.toJson($ctx.args)
}

Using this frontend side filters like {"filter" : "{\"severity\":{\"le\":2}}"} will work again