Use the above flow & call Okta login from WordPress. For showing login button to user please use the following steps
1. Goto WordPress admin site
2. Navigate to Appearance->Widgets
3. Drag Login with Salesforce & drop it on any page. (Here I used Blog Sidebar)
4. You can either add or skip the Title name.
5. It will create a login section with the respective name. Providing a name is optional.
6. Now click on Login with Salesforce link & it will redirect you on IDP page & after entering valid credentials you can able to login into WordPress. Here it shows Salesforce login page.