Hello,
we were solving the issue via e-mails. For other visitors:
You could customize the checkout process. Please see here:
Developing custom dialogs for more information.
You could create a custom step and create a customer by API without connection to any user. The code could look like:
How to create a customer but you exclude the line:
ci.CustomerUserID = ui.UserID;
and leave the CustomerUserID property null.
Best regards,
Helena Grulichova