If you have an MVC site, you have one final step for a successful Connect installation. Since your users will be filling out lead forms on your MVC site (not the admin), you will need to add the Connect (non-Admin) package to your MVC site.
For .Net Core 3.1:
Install-Package BizStream.KenticoToolkit.AspNetCore.WebApp.Connect.KX13
For .Net Framework: Be sure to use the correct version (based on YOUR version of Kentico):
Install-Package BizStream.KenticoToolkit.Connect.KX13
Install-Package BizStream.KenticoToolkit.Connect.K12
Install-Package BizStream.KenticoToolkit.Connect.K11
Install-Package BizStream.KenticoToolkit.Connect.K10
Install-Package BizStream.KenticoToolkit.Connect.K9
Install-Package BizStream.KenticoToolkit.Connect.K82