Troubleshooting: Microsoft SharePoint (On-Premises)
This topic provides solutions to common problems that may occur during the SharePoint (On-Premises) deployment.

Make sure Claims Based Authentication is selected as the preferred mode of authentication for this SharePoint application. From the Windows PowerShell command prompt, enter the following to set the specified user account as an administrator for the site:
$WebAppName = "http://" (http://)"
$wa = get-SPWebApplication $WebAppName
$wa.UseClaimsAuthentication = $true
$wa.Update()

Open the web.config file for this web application and make sure custom errors are turned off in the web.config file.
<system.web>
...
<customErrors mode="Off"/>

Open the web.config file for this web application and add the following line:
(mode=Never)
<microsoft.identityModel>
....
<audienceUris mode="Never"/>

Both Windows Authentication and Okta are chosen as Identity Trust provider. Uncheck Windows Authentication if you want only Okta to act as a trust provider.

Refer to http://technet.microsoft.com/en-us/library/cc288091(v=office.12).aspx. Resetting your IIS server (iisreset) should usually help.

Patch the Sharepoint 2019 server as documented on KB 4484259 and ensure that you are using the https:// prefix for all Sharepoint sites.