For almost all TLDs, you can specify the details for the domain owner, admin-c and billing-c for a domain yourself.
You can use your own domain contacts for the domain owner and admin-c.
Separate contacts are also possible for tech-c and billing-c. As standard, INWX is already selected for these two contact types.
You can use your existing domain contacts (handles). If you need a new contact record, you can create it under the menu item "Domain contacts". You can then assign the contacts accordingly in the ordering process.
Exceptions are .AT and .DE domains. There is no billing-c here, but instead a zone-c that is responsible for the DNS zone. The billing-c selected in the customer area is transmitted to the registry as zone-c and displayed in the Whois.