Signed SAML Auth request to ADFS returns the error 'Element' is an invalid XmlNodeType

Question

I have been trying to create a solution using the ADFS for SSO.

When I try to send the signed request to ADFS I get the below error.

The SSO works fine for the unsigned request.

The decrypted SAMLRequest parameter to the ADFS looks like below:

<saml2p:AuthnRequest ID="_31ff4ded-8a4d-4c09-9e30-9423ef08bd56" Version="2.0" IssueInstant="2023-12-15T09:00:50Z" ProtocolBinding="urn:oasis:names:tc:SAML:2.0:bindings:HTTP-POST" AssertionConsumerServiceURL="https://<server>/saml/acs" xmlns:saml2p="urn:oasis:names:tc:SAML:2.0:protocol">
<saml2:Issuer xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion">
    https://<server>//muse
</saml2:Issuer>
<samlp:NameIDPolicy Format="urn:oasis:names:tc:SAML:1.1:nameid-format:unspecified" AllowCreate="true" xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol"/>
<Signature xmlns="http://www.w3.org/2000/09/xmldsig#">
    <SignedInfo>
        <CanonicalizationMethod Algorithm="http://www.w3.org/TR/2001/REC-xml-c14n-20010315"/>
        <SignatureMethod Algorithm="http://www.w3.org/2001/04/xmldsig-more#rsa-sha256"/>
        <Reference URI="">
            <Transforms>
                <Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature"/>
                <Transform Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/>
            </Transforms>
            <DigestMethod Algorithm="http://www.w3.org/2001/04/xmlenc#sha256"/>
            <DigestValue>
                <!--Removed from sample -->
            </DigestValue>
        </Reference>
    </SignedInfo>
    <SignatureValue>
        <!--Removed from sample -->
    </SignatureValue>
</Signature>

</saml2p:AuthnRequest>

When I try to validate the SAML request using the https://www.samltool.com/validate_xml.php, I get the below error;

Line: 6 | Column: 0 --> Element '{http://www.w3.org/2000/09/xmldsig#}Signature': This element is not expected. Expected is one of ( {urn:oasis:names:tc:SAML:2.0:assertion}Conditions, {urn:oasis:names:tc:SAML:2.0:protocol}RequestedAuthnContext, {urn:oasis:names:tc:SAML:2.0:protocol}Scoping ).