PayPal不发送Webhook，即使它们显示为“已发送”

Question

我正在使用PayPal PHP API设置订阅/定期付款流程。到目前为止，除了一件事-Webhooks之外，一切似乎都可以在沙箱中正常工作。即使Webhook事件显示为在线“发送”，我似乎也从未收到过它们。

我已经检查了webhook事件，并且其中的webhook URL（“传输”->“ webhook_url”）是正确的。如果我在浏览器中访问该URL，则在代码中设置的记录器将正确记录该URL。但是，当贝宝（PayPal）表示已发送Webhook时，我在日志中看不到任何内容（同样，即使它说它已在开发人员控制台中成功发送了Webhook）。

以下是PayPal所说的已发送的Webhook事件之一：

library(shiny)
library(tidyverse)

ui <- fluidPage(

      mainPanel(
        DT::dataTableOutput("flag"),
        actionButton("exclude", "Exclude")

      )
   )

server <- function(input, output) {

  df <- data.frame(id = 1:10, fu_score = 1:10,
                   stringsAsFactors = FALSE)

  if (file.exists("data/prev_exclude.Rda")) {
    load("data/prev_exclude.Rda")
  } else {

    prev_exclude <- data.frame(id = 0, fu_score = 0, stringsAsFactors = FALSE)
    save(prev_exclude, file = "data/prev_exclude.Rda")

  }

  df_flag <- reactive({ 
    df %>%
      anti_join(., prev_exclude, by = c("id", "fu_score"))
  })

  output$flag <- DT::renderDataTable({
    DT::datatable(df_flag(), options = list(paging = FALSE))
  })

  selected_prev <- eventReactive(input$flag_rows_selected, {
    data.frame(id = df_flag()$id[c(input$flag_rows_selected)],
               fu_score = df_flag()$fu_score[c(input$flag_rows_selected)])

  })

  observeEvent(input$exclude, {

    prev_exclude <- isolate(bind_rows(selected_prev(), prev_exclude))
    save(prev_exclude, file="data/prev_exclude.Rda")
    load("data/prev_exclude.Rda")
  })

}

# Run the application 
shinyApp(ui = ui, server = server)

以及实际的Webhook脚本上的前几行代码（尽管我猜这无关紧要，因为我从一开始就进行日志记录，因此它至少应该记录某事当PayPal发送Webhook时）：

{
    "id": "WH-snip-",
    "create_time": "2019-05-06T15:33:38.143Z",
    "resource_type": "sale",
    "event_type": "PAYMENT.SALE.COMPLETED",
    "summary": "Payment completed for EUR 9.99 EUR",
    "resource": {
        "billing_agreement_id": "I-snip-",
        "amount": {
            "total": "9.99",
            "currency": "EUR",
            "details": {
                "subtotal": "9.99"
            }
        },
        "payment_mode": "INSTANT_TRANSFER",
        "update_time": "2019-05-06T15:33:16Z",
        "create_time": "2019-05-06T15:33:16Z",
        "protection_eligibility_type": "ITEM_NOT_RECEIVED_ELIGIBLE,UNAUTHORIZED_PAYMENT_ELIGIBLE",
        "transaction_fee": {
            "value": "0.54",
            "currency": "EUR"
        },
        "protection_eligibility": "ELIGIBLE",
        "links": [
            {
                "href": "https://api.sandbox.paypal.com/v1/payments/sale/-snip-",
                "rel": "self",
                "method": "GET"
            },
            {
                "href": "https://api.sandbox.paypal.com/v1/payments/sale/-snip-/refund",
                "rel": "refund",
                "method": "POST"
            }
        ],
        "id": "-snip-",
        "state": "completed",
        "invoice_number": ""
    },
    "status": "SUCCESS",
    "transmissions": [
        {
            "webhook_url": "-snip- (the URL is 100% correct)",
            "response_headers": {
                "Transfer-Encoding": "chunked",
                "Server": "nginx/1.10.3",
                "Connection": "keep-alive",
                "Date": "Mon, 06 May 2019 15:37:38 GMT",
                "Content-Type": "text/html; charset=UTF-8"
            },
            "transmission_id": "-snip-",
            "status": "SUCCESS",
            "timestamp": "2019-05-06T15:37:25Z"
        }
    ],
    "links": [
        {
            "href": "https://api.sandbox.paypal.com/v1/notifications/webhooks-events/WH-snip-",
            "rel": "self",
            "method": "GET",
            "encType": "application/json"
        },
        {
            "href": "https://api.sandbox.paypal.com/v1/notifications/webhooks-events/WH-snip-/resend",
            "rel": "resend",
            "method": "POST",
            "encType": "application/json"
        }
    ],
    "event_version": "1.0"
}