Not able to add right custom domain form url

We were able to add custom domain successfully to form, but the issue is the slug part. We can’t configure it correctly.

Every time we modify the url and save form, it adds a number ahead of selected slug. e.g. mybusiness.com/xyz-hotel-3

If we remove 3 and save it again then it become mybusiness.com/xyz-hotel-4

It’s kind of a behaviour system remembers the previous url, as it exists in any other form and prevent it from using again, whereas there is no such form with that url.