Using %URL% in custom field

Hello!

I was hoping you could help me map the URL our form is submitted from to a custom field.

I know you can use %URL% to show the URL in the “Lead Source”, but we have a custom field for the URL already setup.

I created a hidden field and mapped it to our custom field. I set the value to to %URL%, but the value displayed in salesforce is simply “http://%URL%”

Any help you can provide would be great.