Storefront server - unable to connct

Has this worked earlier?

No its a new build.

check (and post) eventlog "Citrix delivery Services" onto SF-Server.
There are helpful hints ... mostly.

If  it is a new build then please go through this flowchart: https://support.citrix.com/article/CTX207162

This will systematically check if a load balancer/Netscaler etc is the culprit.

Not using netscaler, or load balancing at the moment.

Error showing in eventvwr

Failed to run discovery
Citrix.Web.DeliveryServicesProxy.ConfigLoader.DiscoveryServiceException, ReceiverWebConfigLoader, Version=3.9.0.0, Culture=neutral, PublicKeyToken=null
An error occurred while contacting the Discovery Service
   at Citrix.Web.DeliveryServicesProxy.ConfigLoader.Discovery.AppendConfigurationFromDiscoveryService(WebReceiverConfigSection section)
   at Citrix.Web.DeliveryServicesProxy.ConfigLoader.Discovery.RunDiscovery(WebReceiverConfigSection configSection)
   at Citrix.Web.Proxy.Filters.DiscoveryComplete.OnAuthorization(AuthorizationContext filterContext)

System.Net.WebException, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel.
Url: https://127.0.0.1/Citrix/App7/discovery
ExceptionStatus: TrustFailure
   at System.Net.HttpWebRequest.GetResponse()
   at Citrix.DeliveryServicesClients.Utilities.HttpHelpers.ReceiveResponse(HttpWebRequest req)
   at Citrix.DeliveryServicesClients.Utilities.HttpHelpers.ReceiveResponse(String url, String token, HttpRequestParameters options, Object requestData, CookieContainer cookieContainer, Boolean overrideLoopback)
   at Citrix.DeliveryServicesClients.Discovery.RequestHandler.DiscoveryHttpRequestHandler.GetDocument(String url)
   at Citrix.DeliveryServicesClients.Discovery.DiscoveryClient.GetDocument(String url)
   at Citrix.Web.DeliveryServicesProxy.ConfigLoader.Discovery.AppendConfigurationFromDiscoveryService(WebReceiverConfigSection section)

System.Security.Authentication.AuthenticationException, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
The remote certificate is invalid according to the validation procedure.
   at System.Net.Security.SslState.StartSendAuthResetSignal(ProtocolToken message, AsyncProtocolRequest asyncRequest, Exception exception)
   at System.Net.Security.SslState.ProcessReceivedBlob(Byte[] buffer, Int32 count, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.ProcessReceivedBlob(Byte[] buffer, Int32 count, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.ProcessReceivedBlob(Byte[] buffer, Int32 count, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.ForceAuthentication(Boolean receiveFirst, Byte[] buffer, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.ProcessAuthentication(LazyAsyncResult lazyResult)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Net.TlsStream.ProcessAuthentication(LazyAsyncResult result)
   at System.Net.TlsStream.Write(Byte[] buffer, Int32 offset, Int32 size)
   at System.Net.ConnectStream.WriteHeaders(Boolean async)

Problem was due to an incorrect Certifiate