While creating a project the Project Manager has the possibility to define how many days before or after closing the project participants can add expenses.
By default, expenses can only be added to ongoing projects. To change this, the Project Manager have to go to the Update Project page and find the Expenses Days field. The number in this field corresponds to the number of days.
For example, if the Project Manager allows users to add expenses 5 days after the closing the project, then he needs to input "5", if 5 days before closing the project then it will be "-5".