I’m guessing that you’re might be using woocommerce. checkout_url is a url query parameter used by woocommerce. Using it as a field name can cause unexpected issues. I’m not saying that this is definitely the issue, but it might cause a problem. To be honest, I’ve never seen this happen with a URL field on any site that I’ve worked on.
Somewhere along the line it has something to do with some type of redirect or rewrite that’s happening based on the URL being part of the $_POST values that are being sent to the server.
Can you give me a list of all the plugins that you’re using on the site? I’d really like to try to recreate this just to see if I can. Have you tried deactivating other plugins or changing themes?
