Unstable result of json decoder

I am trying out json.Decoder and got something strange happening. The same code will NOT produce consistent result. Sometimes it works fine; sometimes it errors: not at beginning of value from calling Decode.

func main() {
    simpleRequest()
}

type FxPair struct {
    CurrencyCodeA int     `json:"currencyCodeA"`
    CurrencyCodeB int     `json:"currencyCodeB"`
    Date          int     `json:"date"`
    RateBuy       float64 `json:"rateBuy"`
    RateSell      float64 `json:"rateSell"`
    RateCross     float64 `json:"rateCross"`
}

func simpleRequest() {
    res, err := http.Get("https://api.monobank.ua/bank/currency")
    if err != nil {
        panic(err)
    }
    defer res.Body.Close()

    decoder := json.NewDecoder(res.Body)
    _, err = decoder.Token() // read the opening square bracket
    if err != nil {
        panic(err)
    }
    var pair FxPair
    for decoder.More() {
        err := decoder.Decode(&pair)
        if err != nil {
            panic(err)
        }
        fmt.Printf("%+v\n", pair) // process a pair
    }
    _, err = decoder.Token() // read the closing square bracket
    if err != nil {
        panic(err)
    }
}