Here is the SOAP login envelope I am stuck on:

<Envelope xmlns="http://schemas.xmlsoap.org/soap/envelope/">
    <Header>
        <LoginScopeHeader xmlns="urn:partner.soap.sforce.com">
            <organizationId>00DJ0000003L9lt</organizationId>
            <portalId>[string?]</portalId>
    

Where do I find our Portal ID?