account numbe r for posting

Usually a user should select an account number in the header of document, for example ARAccount (for Debit). And for example a credit account is saved in Items.
I need to write a fix account number in the object module code. In my case it is 4020 (Income 20%). So if I write Record.Account = 4020 for posting, I get an error. What is the syntax for such kind of record?

It's not recommended. Account numbers need to be in settings or document forms so a user can change them.

But anyway, use FindByCode like in this example:

&AtServer
Procedure OnCreateAtServer(Cancel, StandardProcessing)
Object.Account = ChartsOfAccounts.ChartOfAccounts.FindByCode("4020");
EndProcedure