Submitting form to admin-post.php WordPress

First thank you to @TomJNowell for helping me to figure this out. There was a few misleading assumptions I made that had me making this harder than it needed to be.

There’s no need to post to admin-post, keeping the action blank to submit to the current page is perfectly fine.

I don’t seem to need to add the url parameter that wordpress automatically adds either.

The url parameters do not get placed in the url bar, leading me to believe it was not getting posted. (Assumption) Upon adding this to the file:

<?php
    if(isset($_POST['submit'])){
        echo "Submit detected!";
        print_r($_POST);
    }
?>

I was able to see that the input data was very much getting posted and I just need to take it from this point.

Thanks again !