How to use the @here/olp-sdk-dataservice-api.QueryApi.quadTreeIndex function in @here/olp-sdk-dataservice-api

private async downloadIndex(indexRootKey: QuadKey): Promise {
        let dsIndex: QueryApi.Index;
        const queryRequestBuilder = await this.getRequestBuilder("query");
        const version = await this.getLatestVersion();

        dsIndex = await QueryApi.quadTreeIndex(queryRequestBuilder, {
            version,
            layerId: this.layerId,
            quadKey: utils.mortonCodeFromQuadKey(indexRootKey).toString(),
            depth: this.indexDepth
        });

        return this.parseIndex(indexRootKey, dsIndex);
    }