Tableau Cloud - Exception processing SAML Response. Root cause: Failed to decrypt EncryptedData

Question

Objective

I'm trying to get a Tableau SAML connection working, where my software is the IDP.

What I did

I generated a certificates using openssl req -x509 -sha256 -nodes -days 365 -newkey rsa:2048 -keyout privateKey.key -out certificate.crt

I'm using this online tool to generate a IDP metadata file. https://www.samltool.com/idp_metadata.php and would populate the fields, and put int he public and private key in the boxes indicated below.

Error I get

When I test the functionality of the SAML, using the tableau "test connection", I get the following error in THEIR logs.

2023-10-23T19:29:52.811Z |    ERROR | Exception processing SAML Response. Root cause: Failed to decrypt EncryptedData
2023-10-23T19:29:52.807Z |     INFO | Operation: Response
Issuance: REMOTE
Local entity ID: https://sso.online.tableau.com/public/sp/metadata/REDACTED
Remote entity ID: https://REDACTED/saml
Recipient: https://sso.online.tableau.com/public/sp/SSO/REDACTED
Binding: urn:oasis:names:tc:SAML:2.0:bindings:HTTP-POST
Message: <?xml version="1.0" encoding="UTF-8"?><samlp:Response xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol" Consent="urn:oasis:names:tc:SAML:2.0:consent:unspecified" Destination="https://sso.online.tableau.com/public/sp/SSO/REDACTED" ID="REDACTED" IssueInstant="2023-10-23T19:29:52Z" Version="2.0">
    <Issuer xmlns="urn:oasis:names:tc:SAML:2.0:assertion">https://REDACTED/saml</Issuer>
    <samlp:Status>
        <samlp:StatusCode Value="urn:oasis:names:tc:SAML:2.0:status:Success"/>
    </samlp:Status>
    <EncryptedAssertion xmlns="urn:oasis:names:tc:SAML:2.0:assertion">
        <EncryptedData xmlns="http://www.w3.org/2001/04/xmlenc#" Id="ED" Type="http://www.w3.org/2001/04/xmlenc#Element">
            <EncryptionMethod Algorithm="http://www.w3.org/2001/04/xmlenc#aes256-cbc"/>
            <ds:KeyInfo xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
                <EncryptedKey Id="EK" xmlns="http://www.w3.org/2001/04/xmlenc#">
                    <EncryptionMethod Algorithm="http://www.w3.org/2001/04/xmlenc#rsa-oaep-mgf1p"/>
                    <ds:KeyInfo xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
                        <ds:KeyName/>
                        <ds:X509Data>
                            <ds:X509Certificate>REDACTED</ds:X509Certificate>
                        </ds:X509Data>
                    </ds:KeyInfo>

I'm using a fairly stock setup of saml_idp gem in ruby on rails. Which I'm signing the response back with the certificate I downloaded from Tableau.

Any Ideas?

Any ideas would be helpful. Thank You.