Me too

Hi Sam,

You were probably better off starting a new thread opposed to dredging up one that was this old!

Regardless, you can't use the FormsSubmissionFinalized event. What you'll need to do is add a custom DataSubmissionService (EPiServer.Forms.Core.Internal) implementation and override the BuildReturnResultForSubmitAction method, as per this example:

public class CustomDataSubmissionService : DataSubmissionService
{
    protected override SubmitActionResult BuildReturnResultForSubmitAction(bool isJavaScriptSupport, bool isSuccess,
        string message, HttpContextBase httpContext, FormContainerBlock formContainer = null,
        Dictionary<string, object> additionalParams = null, SubmissionInfo submissionInfo = null,
        Submission submission = null, bool isProgressiveSubmit = false, string redirectUrl = "")
    {
        if (!string.IsNullOrEmpty(message))
        {
            message = $"{message}<p>Example.</p>";
        }

        return base.BuildReturnResultForSubmitAction(isJavaScriptSupport, isSuccess, message, httpContext,
            formContainer, additionalParams, submissionInfo, submission, isProgressiveSubmit, redirectUrl);
    }
}

You can easily switch out the default implementation:

[InitializableModule]
public class FormsInitialization : IConfigurableModule
{
    public void ConfigureContainer(ServiceConfigurationContext context)
    {
        context.ConfigurationComplete += (o, e) =>
        {
            context.Services.AddSingleton<DataSubmissionService, CustomDataSubmissionService>();
        };
    }

    public void Initialize(InitializationEngine context)
    {
    }

    public void Uninitialize(InitializationEngine context)
    {
    }
}

This will append "<p>Example.</p>" to the end of your success message (regardless of the form or the message) but it hopefully gives you enough to get started.