First is you IdP set to active?
You should also of added the SAML.Startup microflow to the application Start-up Microflow? This microflow will initialise the custom request handler /SSO/, validates all IdP configurations, and prepares any configuration entities required during the configuration.
You would also need to add the following html to your index.html file. Your login.html file should already redirect to your index.html page.
<meta http-equiv="refresh" content="0;URL=/SSO/" />
Certain constants also need to be updated in accordance with your project to make the SSO setup work. Below is a list of these constant values:
• SAML20.BindingURI_Redirect : false
• SAML20.DefaultLoginPage : /index.html
• SAML20.DefaultLogoutPage : /SSO/
• SAML20.SSOLandingPage : /index3.html
Did set access in your Sprintr environment on the Network tab (Path Based Access Restrictions) to /SSO/?