Unfortunately, ternary expressions don’t work for display format.
I don’t know of a cleaner way to do it as I’m not too familiar with the reporting tags. But seeing as the ticket entity is either Table or Orders, try this for the ticket amount. Only one will return a value. I don’t know the cost of the queries when doubling-up on reporting tags.
{REPORT TICKET DETAILS:T.TotalAmount:(TEN.Tables=$1) and (TS.Status=Unpaid)}{REPORT TICKET DETAILS:T.TotalAmount:(TEN.Orders=$1) and (TS.Status=Unpaid)}