Hi Hans,
You need to develop an Extension and publish it in your BC.
This is an example of what you can do to transfer this field:
Create a codeunit and add a subscriber event to the OnAfterValidateEvent of the "Sell-to Customer No." field.
This code will be executed every time the "Sell-to Customer No." field is updated.
[EventSubscriber(ObjectType::Table, Database::"Sales Header", 'OnAfterValidateEvent', 'Sell-to Customer No.', false, false)]
local procedure ValidateEORIOnSalesHeaderOnAfterValidateEventSelltoCustomerNo(var Rec: Record "Sales Header")
var
Customer: Record Customer;
begin
Customer.Get(Rec."Sell-to Customer No.");
Rec.Validate("EORI Number", Customer."EORI Number");
end;
Notice that I have not found an equivalent field for "EORI Number" in the "Sales Header" table, so maybe you need to create it by a tableextension.
