How to have a custom pop up thank you message after form submission

Is it possible to edit the source code without hosting the form files on my own server? I'm looking to add a pop-up thank you message, but prefer to use the HTML embed on my web page. Thanks!

Is it possible to edit the source code without hosting the form files on my own server?

No you can't. You can only edit the source code if you will use the full source on your own website.

But you can use the default embed code of your form on your website and then just use the custom URL redirect Thank You page so that you can have a custom pop Thank You message once it was redirected to your website page.

User guide: Redirecting-Users-to-a-Different-Page

Hope this help. Let us know how we can be of further assistance.

Thank you.