"ERROR" A member with this email address already exists. Try a different email

I’m having trouble with
A custom Sign up form

Working in
Wix Studio Editor.

Site link

What I’m trying to do
If you fill in the form and try and submit it, you will receive the error “A member with this email address already exists. Try a different email.” any email I try will result in this error. none of the emails I use are in the customer backend.

What I’ve tried so far
Ive checked the backend for the emails I’ve used.

Ive checked my setting.

Ive delete the field and created a new one.

Try this:

Test the published site in an incognito/private browser using a completely new email address.

After receiving the error, check Dashboard → Site Members, not only Customers or Contacts.

If the new member appears there, the first submission succeeded and something is triggering registration a second time.

Does the default form work ?