AD FS 2.0, Event 303

I am attempting to setup ADFS using the SAML 2.0 Single Sign-On v0.9.2 and am encountering the following error:

The Federation Service encountered an error while processing the SAML authentication request.

Additional Data
Exception details:
Microsoft.IdentityModel.Protocols.XmlSignature.SignatureVerificationFailedException: MSIS0037: No signature verification certificate found for issuer ‘https://saufoundation.wpengine.com/wp-content/plugins/saml-20-single-sign-on_/saml/www/module.php/saml/sp/metadata.php/1’.
at Microsoft.IdentityServer.Protocols.Saml.Contract.SamlContractUtility.CreateSamlMessage(MSISSamlBindingMessage message)
at Microsoft.IdentityServer.Service.SamlProtocol.SamlProtocolService.CreateErrorMessage(CreateErrorMessageRequest createErrorMessageRequest)
at Microsoft.IdentityServer.Service.SamlProtocol.SamlProtocolService.ProcessRequest(Message requestMessage)

I have a purchased SSL cert available to upload, but how? I’ve already exported the file to include the private key. Is this single file uploaded as both the “Signing Certificate” and “Signing Private Key”?