From what I understand, when you enter a customer number into the ShipTo field you want the Customer Function (CustomerMasterPartner) association to be created and associated with the customer(CustomerMaster) and SalesOrder.
If that's correct, then you'll want a microflow:
If that sounds right you can find further details here:
thanks for your reply, yes Ship to is a reference to customer , each customer can have as Shipt to himself or in addition n others, as example here below 5678 is linked to the customer 1234
and no I don twant that details are popoulated during typing, simply when the customer number is inserted and select then on the othe side his name should be derived.
I hope it s clear