How to fix when Okta SAML authorization succeeds but returns to a Splunk 404 error?

We configured Splunk Enterprise 6.4.2 for SAML authentication following the [latest documentation][1], and while the basic authentication & authorization succeeds, the SSO process then drops the user into a Splunk URI that is a 404 error: https://splunkserver:8000/en-US/secret/endpoint/postResponse 404 Not Found Return to Splunk home page Page not found! View more information about your request (request ID = [snip]) in Search This page was linked to from https://[SSO.provider]/app/splunk/[token]/sso/saml. You are using [splunk]:8000, which is connected to splunkd @[snip] at https://127.0.0.1:8089 on Mon Aug 8 16:17:18 2016. How do I fix this? [1]: http://docs.splunk.com/Documentation/Splunk/6.4.3/Security/ConfigureSSOOkta