Why can’t overlapping dates with a previous payment certificate be selected?

The time period (start and end date) of the work items specified in the new payment certificate can’t overlap with the time period of any matching work item previously included in an earlier payment certificate — the purpose of this restriction is to ensure the same work period isn’t counted twice for the same item, and to maintain a logical, continuous timeline for the work’s execution across successive payment certificates.

When this conflict is detected, a message appears identifying the affected work item:

“The start date for ‘[work item title]’ #[code] can’t overlap with previous payment certificates.”