Amplify-cli: How to insert an array of strings on a type with a @key set on that field?

[PeteDuncanson]

* Please describe which feature you have a question about? *

I have a type in my schema that accepts an array of strings and a @key on that array to help be search by it (at least that is the idea). However when I try to create that type using a GraphQL mutation I get an error when trying to insert the values for the string array. Am I doing something wrong?

* Provide additional details*

Sample schema:

type Area   
  @model
  # If I remove this key everything works as it should I think, but I lose the key!
  @key(
    name: "byPostcode"
    fields: ["postcodes"]
    queryField: "testAreaByPostcode"
  )  {
  name: String
  postcodes: [String!]!
}

Mutation run in GraphiQL:

mutation AddLeeds($input: CreateAreaInput! ) {
  createArea( input: $input) {
    id
    name
  }
}

Query input:

{ 
  "input": {
    name: "Leeds",
    postcodes: ["LS1", "LS2", "LS3"]    
  }
}

Running the above gives me this error:

{
  "data": {
    "createArea": null
  },
  "errors": [
    {
      "message": "Invalid attribute value type",
      "errorType": "DynamoDB:ValidationException",
      "data": null,
      "errorInfo": null,
      "path": [
        "createArea"
      ],
      "locations": [
        {
          "line": 4,
          "column": 3,
          "sourceName": "GraphQL request"
        }
      ]
    }
  ]
}

What gives?

[nikhname]

@PeteDuncanson We do not support inserting an array of strings on keys in this way. I have marked this as a bug as we should validate this at compile time and provide a better error message.

[stwatanabe]

I'm facing same issue.
Im my case, tagList is type of [String!]
When send a mutate request to mock api server, the message returned from backend.

mutation MyMutation {
  createVodAsset(input: {title: "", description: "",  tagList: ["aaa","ddd"]}) {
    id
  }
}

The result of a request on backend

Error while executing Local DynamoDB
{
    "version": "2018-05-29",
    "operation": "PutItem",
    "key": {
        "id": {
            "S": "69cbdff5-f619-4014-a46b-742dbd41cbf3"
        }
    },
    "attributeValues": {
        "title": {
            "S": ""
        },
        "description": {
            "S": ""
        },
        "tagList": {
            "L": [
                {
                    "S": "aaa"
                },
                {
                    "S": "ddd"
                }
            ]
        },
        "id": {
            "S": "69cbdff5-f619-4014-a46b-742dbd41cbf3"
        },
        "createdAt": {
            "S": "2020-12-18T06:43:21.132Z"
        },
        "updatedAt": {
            "S": "2020-12-18T06:43:21.132Z"
        },
    },
    "condition": {
        "expression": "attribute_not_exists(#id)",
        "expressionNames": {
            "#id": "id"
        }
    }
}
ValidationException: Invalid attribute value type