Salesforce Identity for Enablement Setup and Login Issues

Fully review the Authentication Providers for Your Enablement Site documentation and please note the following order of operations is extremely important:

1. Configure Salesforce Identity for Enablement in your production org.

Note:  The following step is important so please carefully read through the documentation to choose the appropriate URL for your Trailhead authentication page to ensure the remaining steps are configured correctly.
 

2. Configure Salesforce Identity for Enablement and be absolutely sure that you're inputting the correct "Login Page URL" before submitting to activate.

Note: After submitting the configuration in this step, it's not possible to change or edit the "Login Page URL." In order to change this value you will need to contact Salesforce Support. Please ask your Support case owner to reference the internal information section of this article for more details.
 

If your organization has implemented Restrict Login IP Ranges in the Enhanced Profile User Interface and users are encountering the following error in their browser's URL on attempting to access myTrailhead:
 

error=redirect_uri_mismatch&error_description=redirect_uri%20must%20match%20configuration

Add the following Trailhead outbound IP addresses to affected user's assigned profile 'Login IP Ranges' and as outlined in the Salesforce IP Addresses and Domains to Allow :

52.205.40.33

52.205.41.207

52.205.38.38

52.6.127.225

34.217.238.68

52.13.162.184

52.36.203.77

52.43.127.242

54.245.10.179

100.20.235.153

error=invalid_client_id&error_description=client%20identifier%20invalid

Make sure the running user is assigned the connected app through their profile.