Post HTML form to specific method

I have a Razor Page template with an HTML form. I wish to trigger a specific method on the post event.

The form is as follows:

<form method="post" asp-page-handler="Edit">
    <input type="text" name="firstName" />
    <input type="submit" value="Submit" />
</form>

And the page model:
public class TestPageModel : RazorPageModel<TestPage>
{

...
    public void OnPostEdit(string firstName)
    {
        var s = firstName;
    }
}

According to ASP .NET Core documentation and handler naming conventions, asp-page-handler="Edit" should trigger the OnPostEdit method.

If I add the general OnPost method, it will be triggered on the form submit:

        public void OnPost(string firstName)
        {
            OnGet();
        }

But I have several forms on the page template, and each needs its own method.

I cannot find any Optimizely documentation regarding this, and I suspect the issue is due to Optimizely routing.

Has anybody solved this?