If your company would like to make the merchant field required in an expense, as an administrator, you can enable the 'Merchant field required in an expense' by following the steps below:
Go to Admin, select Advanced settings. Under the Expense Settings column, add a check mark in 'Make merchant field required in an expense'
2. Click Save, once done.
Note: The user will not be allowed to submit the expense when the merchant field is blank.