client := tinkoff.NewClient(terminalKey, terminalPassword)

router.POST("/payment/notification/tinkoff", func(c *gin.Context) {
    notification, err := client.ParseNotification(c.Request.Body)
    if err != nil {
        handleInternalError(c, err)
        return
    }

    // handle notification, e.g. update payment status in your DB

    // response well-formed body back on success. If you don't do this, the bank will send notification again later
    c.String(http.StatusOK, client.GetNotificationSuccessResponse())
}

req := &tinkoff.InitRequest{
    Amount:      60000,
    OrderID:     "123456",
    CustomerKey: "123",
    Description: "some really useful product",
    RedirectDueDate: tinkoff.Time(time.Now().Add(4 * 24 * time.Hour)),
    Receipt: &tinkoff.Receipt{
        Email: "[email protected]",
        Items: []*tinkoff.ReceiptItem{
            {
                Price:    60000,
                Quantity: "1",
                Amount:   60000,
                Name:     "Product #1",
                Tax:      tinkoff.VATNone,
            },
        },
        Taxation: tinkoff.TaxationUSNIncome,
        Payments: &tinkoff.ReceiptPayments{
            Electronic: 60000,
        },
    },
    Data: map[string]string{
        "custom data field 1": "aasd6da78dasd9",
        "custom data field 2": "0",
    },
}
res, err := client.Init(req)
// ...
fmt.Println("payment form url: %s", res.PaymentPageURL)

req := &tinkoff.InitRequest{
    Amount:      1000,                 // минимум 1000 копеек 
    OrderID:     "123456",
    Data: map[string]string{"": "",},  // nil - недопустим.
res, err := client.Init(req)
gqr := &tinkoff.GetQrRequest{
    PaymentID: res.PayID,
}
resQR, errQ := client.GetQR(gqr)

req := &tinkoff.CancelRequest{
    PaymentID: "66623",
    Amount: 60000,
}
res, err := client.Cancel(req)

res, err := client.GetState(&tinkoff.GetStateRequest{PaymentID: "3293"})
// ...
if res.Status == tinkoff.StatusConfirmed {
    fmt.Println("payment completed")
}

res, err := client.Confirm(&tinkoff.ConfirmRequest{PaymentID: "3294"})
// ...
if res.Status == tinkoff.StatusConfirmed {
    fmt.Println("payment completed")
}

res, err := c.Resend()
// ...
fmt.Println("resend scheduled for %d notifications", res.Count)

type myCouponUpgradeRequest struct {
  tinkoff.BaseRequest
  PaymentID string `json:"PaymentId"`
  Coupon    string `json:"coupon"`
}
httpResp, err := client.PostRequest(&myCouponUpgradeRequest{PaymentID: "3293", Coupon: "whatever"})