AWS Amplify GraphQL API: Unable to retrieve the first 10 items (with `beginsWith` filter)

Here’s my schema:

type Post
  @model {
  createdAt: AWSDateTime!
  hash: String!
  version: Int
    @default(value: "0")
    @index(name: "byVersion", sortKeyFields: ["createdAt"])
}

Here’s the generated query that AWS Amplify generates:

export const postsByVersionAndCreatedAt = /* GraphQL */ `
  query postsByVersionAndCreatedAt(
    $version: Int!
    $createdAt: ModelStringKeyConditionInput
    $sortDirection: ModelSortDirection
    $filter: ModelPiecePostFilterInput
    $limit: Int
    $nextToken: String
  ) {
    postsByVersionAndCreatedAt(
      version: $version
      createdAt: $createdAt
      sortDirection: $sortDirection
      filter: $filter
      limit: $limit
      nextToken: $nextToken
    ) {
      items {
        hash
        id
        version
        __typename
      }
      nextToken
      __typename
    }
  }
`;

Finally, here’s my attempt to retrieve the first 10 items:

const postsByVersionAndCreatedAtResult = await API.graphql({
  authMode: GRAPHQL_AUTH_MODE.AWS_IAM,
  query: postsByVersionAndCreatedAt,
  variables: {
    filter: {
      hash: {
        beginsWith: e.target.value,
      },
    },
    limit: 10,
    sortDirection: "DESC",
    version: 0,
  },
});

This works, but I only get 3 items, not 10 items. I thought creating an @index in the schema would solve this problem, but it doesn’t! What must I do/change?