[AC-1783] PayPal IPN Changes (#3404)

* Reverted changes to the domain for the PayPal IPN client, and added more logging

* Removing User-Agent as it wasn't in the IPN client previously

src/Billing/Utilities/PayPalIpnClient.cs

@@ -15,9 +15,9 @@ public class PayPalIpnClient
     public PayPalIpnClient(IOptions<BillingSettings> billingSettings, ILogger<PayPalIpnClient> logger)
     {
         var bSettings = billingSettings?.Value;
-        _ipnUri = new Uri(bSettings.PayPal.Production ? "https://ipnpb.paypal.com/cgi-bin/webscr" :
-            "https://ipnpb.sandbox.paypal.com/cgi-bin/webscr");
         _logger = logger;
+        _ipnUri = new Uri(bSettings.PayPal.Production ? "https://www.paypal.com/cgi-bin/webscr" :
+            "https://www.sandbox.paypal.com/cgi-bin/webscr");
     }
 
     public async Task<bool> VerifyIpnAsync(string ipnBody)
@@ -29,19 +29,16 @@ public async Task<bool> VerifyIpnAsync(string ipnBody)
             throw new ArgumentException("No IPN body.");
         }
 
-        var request = new HttpRequestMessage
-        {
-            Method = HttpMethod.Post,
-            RequestUri = _ipnUri
-        };
-        _httpClient.DefaultRequestHeaders.Add("User-Agent", "CSharp-IPN-VerificationScript");
+        var request = new HttpRequestMessage { Method = HttpMethod.Post, RequestUri = _ipnUri };
         var cmdIpnBody = string.Concat("cmd=_notify-validate&", ipnBody);
         request.Content = new StringContent(cmdIpnBody, Encoding.UTF8, "application/x-www-form-urlencoded");
         var response = await _httpClient.SendAsync(request);
         if (!response.IsSuccessStatusCode)
         {
+            _logger.LogError("Failed to receive a successful response from PayPal IPN verification service. Response: {Response}", response);
             throw new Exception("Failed to verify IPN, status: " + response.StatusCode);
         }
+
         var responseContent = await response.Content.ReadAsStringAsync();
         if (responseContent.Equals("VERIFIED"))
         {
@@ -53,6 +50,7 @@ public async Task<bool> VerifyIpnAsync(string ipnBody)
             _logger.LogWarning("Received an INVALID response from PayPal: {ResponseContent}", responseContent);
             return false;
         }
+
         _logger.LogError("Failed to verify IPN: {ResponseContent}", responseContent);
         throw new Exception("Failed to verify IPN.");
     }