Error during tentacle setup: The remote certificate is invalid according to the validation procedure

We are trying to configure a new polling tentacle but we are receiving a certificate error. This happens in the step where you provide the URL of the Octopus server and username and password to verify your credentials. We have tried to configure this on several servers, including in the actual Octopus server itself and we receive the same error each time. A few weeks ago we did rename the server that Octopus is installed on, but we were able to remove and reinstall the tentacles then without any problems. We are running Octopus version 3.2.21

Here is the full error message:
Error: Unable to connect to the Octopus Deploy server. See the inner exception for details.
System.Exception: Unable to connect to the Octopus Deploy server. See the inner exception for details. —> System.Net.WebException: The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel. —> System.Security.Authentication.AuthenticationException: 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.StartSendBlob(Byte[] incoming, Int32 count, 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.StartSendBlob(Byte[] incoming, Int32 count, 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.StartSendBlob(Byte[] incoming, Int32 count, 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.StartSendBlob(Byte[] incoming, Int32 count, 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)
— End of inner exception stack trace —
at System.Net.HttpWebRequest.GetResponse()
at Octopus.Client.OctopusClient.DispatchRequest[TResponseResource](OctopusRequest request, Boolean readResponse) in Y:\work\refs\tags\3.2.21\source\Octopus.Client\OctopusClient.cs:line 479
at Octopus.Client.OctopusClient.Get[TResource](String path, Object pathParameters) in Y:\work\refs\tags\3.2.21\source\Octopus.Client\OctopusClient.cs:line 85
at Octopus.Client.OctopusClient.EstablishSession() in Y:\work\refs\tags\3.2.21\source\Octopus.Client\OctopusClient.cs:line 313
— End of inner exception stack trace —
at Octopus.Client.OctopusClient.EstablishSession() in Y:\work\refs\tags\3.2.21\source\Octopus.Client\OctopusClient.cs:line 336
at System.Lazy1.CreateValue() at System.Lazy1.LazyInitValue()
at Octopus.Client.OctopusClient.get_RootDocument() in Y:\work\refs\tags\3.2.21\source\Octopus.Client\OctopusClient.cs:line 45
at Octopus.Manager.Tentacle.TentacleConfiguration.SetupWizard.TentacleSetupWizardModel.VerifyCredentials(ILog logger) in Y:\work\refs\tags\3.2.21\source\Octopus.Manager.Tentacle\TentacleConfiguration\SetupWizard\TentacleSetupWizardModel.cs:line 302

Hi Clayton,

Thanks for getting in touch! I am a bit confused how this would have come about. To get to the bottom of it I would need a tonne of information.
How do you feel about scheduling a call so I can see whats up and get an understanding of what changed for you.
https://calendly.com/octopusdeploy/supportcall

Thanks!
Vanessa

Hi Clayton,

I saw you cancelled the screenshare. Did you sort this out? Would you like some assistance via email instead?

Vanessa

We figured this out… we were using the wrong URL to connect to. We were attempting to connect to the specific port that Octopus was using for polling tentacles, rather than the URL of the octopus admin site. We are up and going now… thanks Vanessa!

Hi Clayton,

Great to hear it! I will keep this in mind for those who get this error in the future as a possible trouble shoot!

Vanessa