In addition to sending an external URL through emails, Online Forms can also be published in the Web Store to allow shoppers to visit a Web Store, fill up the form, and submit them from the site.
These published forms are like Information Items, and you can also use its URL to create a hyperlink on the site to direct shoppers to the form.
The only requirement for this is to assign a Site Category/Tab to the published form in order to have it display in the Web Store.
If for some reason, the Site Category is set to inactive, or removed, the published form can still be accessed through its URL. But when a shopper submits the form, they will receive an error message: This category is no longer available.
To resolve this error, edit the Published Form under Lists > Web Site > Publish Forms. Under the Basic tab, make sure that the Site Category is updated with a valid Site Category/Tab, then save the changes.