Inbound SSO denied - No connection string was provided!

I am trying to do a single sign-on to a vender site. I’m testing from my local development server. It throws an error on their end and they are able to capture it so they believe there were no whitelisting or firewall issues preventing the connection. I have SAML trace turned on and its showing everything was a success. They haven’t giving me much information about the error and I can’t find any specific information about it. Can anyone help? Below is the exception:

8:21:26.858 PM
{ [-]
@mt: Manually raised event for exception
@t: 2019-07-19T20:21:26.8586205Z
@x: WebMD.Registration.SSO.Exceptions.NoConnectionStringProvidedException: Inbound SSO denied - No connection string was provided!
ExceptionDetail: { [-]
HResult: -2146233088
Message: Inbound SSO denied - No connection string was provided!
StackTrace: at WebMD.Registration.SSO.Connections.SSOInboundConnection.ValidateRawConnectString(String rawConnectionString) at WebMD.Registration.SSO.Connections.SSOInboundConnection.Process()
Type: WebMD.Registration.SSO.Exceptions.NoConnectionStringProvidedException
SourceContext: ErrorLog
client_connected: true
context_hash: 435A614DBF5CD12E
context_time: 0.0312279
cs_Referrer: http://localhost:50582/
cs_User_Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/64.0.3282.186 Safari/537.36
cs_method: POST
cs_uri_query: -
cs_uri_stem: /ghcscw/connect.aspx
event_id: efedde89-324e-4f56-9fd7-d667d751cdef
event_time: 2019-07-19T13:21:26.8586205-07:00
event_type: HandledApplicationErrorEvent
logtype: Inbound SSO failed: NoConnectionStringProvided
message: Inbound SSO failed: NoConnectionStringProvided
phm_version: 19.717.7542.0
process_time: 46886.2052325
raw_url: /ghcscw/connect.aspx
severity: Low
severity_ex: Low
sponsorid: 13826
sponsortlid: 697
src_ip_enc: e2:nMtizu8rDQdKWq01a09z9l7PkAhluYvdT+RMOWseDMQ=|0r/BAmXLe3+UQXkdk35a4w==|sMEelaZp+IzbGNl+DOg0Qw==
thread_id: 115
unthrown_stack: { [+]
web_identifier: 4UTU9TSYT9
wmLanguage: en-US
wmSponsorID: 13826
x-webmd-correlation-id: 42d12f7f-e9dc-46ab-917c-16b60eb4ff4c

I’m not sure what connection string they’re referring to.
Is it a database connection string not configured at their end?
It’s very hard to debug this type of issue without more assistance from their end.