I would like to ask, is there a free (preferably) system (add as a separate web application on the website) to work with clients?
What you need:
The administrator creates a login/password for the client, the client page is created, in which the administrator enters the order (e.g., made of 30% of the order amount of the order so-and-so... etc).
The customer logs on and enters their data only on their page, where monitors work.
that's about as...