The company either gives allowance and demands invoices against it to settle the balance afterwards, or to give an allowance without demanding any invoices and doesn’t care what you do with it.
If it is the first, you must tell them that you had stayed with friends and dined on their expenses.
If it is the second, you can keep it without telling them.

What is the jurisdiction on an employee who is touring on company’s expense. However he hides his actual accomodation & lives with friends & relatives but gets fixed budget to spend. So is he allowed to use the money which he saves from this budget on himself? If not? Mention a scenario in which its halaal.