Unable to configure PayPal Smart Payment Buttons

Hello All,
   I am getting the below error when configuring PayPal Smart Payment Buttons after providing the Client ID and Secret from an App that was created using Sandbox account.

Payments.PayPalSmartPaymentButtons error:
One or more errors occurred. (A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.)

Any help is greatly appreciated as we want to go live asap.

Below is the full message from the logs:

System.AggregateException: One or more errors occurred. (One or more errors occurred. (A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.))
---> System.AggregateException: One or more errors occurred. (A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.)
---> System.Net.Http.HttpRequestException: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.
---> System.Net.Sockets.SocketException (10060): A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.
   at System.Net.Http.ConnectHelper.ConnectAsync(String host, Int32 port, CancellationToken cancellationToken)
   --- End of inner exception stack trace ---
   at System.Net.Http.ConnectHelper.ConnectAsync(String host, Int32 port, CancellationToken cancellationToken)
   at System.Net.Http.HttpConnectionPool.ConnectAsync(HttpRequestMessage request, Boolean allowHttp2, CancellationToken cancellationToken)
   at System.Net.Http.HttpConnectionPool.CreateHttp11ConnectionAsync(HttpRequestMessage request, CancellationToken cancellationToken)
   at System.Net.Http.HttpConnectionPool.GetHttpConnectionAsync(HttpRequestMessage request, CancellationToken cancellationToken)
   at System.Net.Http.HttpConnectionPool.SendWithRetryAsync(HttpRequestMessage request, Boolean doRequestAuth, CancellationToken cancellationToken)
   at System.Net.Http.RedirectHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
   at System.Net.Http.DiagnosticsHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
   at System.Net.Http.HttpClient.FinishSendAsyncBuffered(Task`1 sendTask, HttpRequestMessage request, CancellationTokenSource cts, Boolean disposeCts)
   at BraintreeHttp.HttpClient.Execute[T](T req)
   --- End of inner exception stack trace ---
   at System.Threading.Tasks.Task.ThrowIfExceptional(Boolean includeTaskCanceledExceptions)
   at System.Threading.Tasks.Task`1.GetResultCore(Boolean waitCompletionNotification)
   at System.Threading.Tasks.Task`1.get_Result()
   at PayPal.Core.PayPalHttpClient.AuthorizationInjector.fetchAccessToken()
   at PayPal.Core.PayPalHttpClient.AuthorizationInjector.Inject(HttpRequest request)
   at BraintreeHttp.HttpClient.Execute[T](T req)
   --- End of inner exception stack trace ---
   at System.Threading.Tasks.Task.ThrowIfExceptional(Boolean includeTaskCanceledExceptions)
   at System.Threading.Tasks.Task`1.GetResultCore(Boolean waitCompletionNotification)
   at System.Threading.Tasks.Task`1.get_Result()
   at Nop.Plugin.Payments.PayPalSmartPaymentButtons.Services.ServiceManager.HandleCoreRequest[TRequest,TResult](PayPalSmartPaymentButtonsSettings settings, TRequest request)
   at Nop.Plugin.Payments.PayPalSmartPaymentButtons.Services.ServiceManager.<>c__DisplayClass29_0.<CreateWebHook>b__0()
   at Nop.Plugin.Payments.PayPalSmartPaymentButtons.Services.ServiceManager.HandleFunction[TResult](PayPalSmartPaymentButtonsSettings settings, Func`1 function)

This could be a problem with your environment.  Are you using a hosting service?  They may not allow you to connect to servers outside their network.  (You may need to call the hosting support to get more details / workaround)

Yes, I am using IONOS shared hosting. I called them and they are saying they do not see any calls being blocked. What specifics should I ask? Any ports that needs to be opened?

Maybe this can help
https://www.ionos.co.uk/help/hosting/net/script-examples-for-establishing-external-http-connections-windows/

Also, I see related issue with IONOS posted here, but no response.
https://www.nopcommerce.com/en/boards/topic/81742/connectivity-issues-with-plugins-when-ssl-is-enabled

After talking to IONOS support they gave me the below link to add the proxy to web.config file. As soon as I add the proxy to the web.config, I am getting the below error. Any thoughts?

Proxy info: https://www.ionos.com/help/index.php?id=4426
Error: HTTP Error 500.0 - ASP.NET Core  IIS hosting failure(in-process)