Hi, the reason you are getting the pop up window, is that you are attempting to use the form in such a way that Webflow is to process the form submissions. You have set no Action property up for the form, that specifies which external URL PHP or other file, will be processing the form. When there is no Action property set, then the Webflow.js script assumes you will have Webflow save the form data in Webflow.
When Webflow tries to look up your site to see if it is an active site, it looks at your data-wf-site id:
data-wf-site=“530cebcb99d6f99347837487” (or whatever your site id is on export)
If the script cannot find this element, or if it cannot find your active site in Webflow with that id, then that alert message will be shown. This data-wf-site=“xxx” id is exported with every site, and is an attribute of the HTML element
Please check out the following article about the elements needed in the exported forms, depending on whether you are hosting the forms on Webflow, or from your external server.
Then after reading that info, if you still have questions, let us know.