You will have to convert each report To Number (TN). The proper syntax is TN('<x>')
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Your almost there. It should be:
[=F(TN(’{REPORT ORDER DETAILS:O.ExactTotal.Sum:(ODI=True) AND (TY=Food Drink Ticket) AND (MG=Starlight Bar) OR (TY=Bistro Food) AND (MG=Starlight Bar)}’)+TN(’{REPORT ORDER DETAILS:O.ExactTotal.Sum:(ODI=True) AND (TY=Bistro Staff Food) AND (MG=Starlight Bar)}’),‘0.00’)]
The ,‘0.00’ may or may not be necessary. Sometimes a calculation is done it will display the least amount of characters as possible. Meaning a number you want to read as 10.00 will be displayed as 10. The ,‘0.00’ will force it to display the .00…Or if the calculation is longer than 2 digits past (to the right) the decimal, it will force it to 2 places.
Here is the first link I could find about the F (Format) - the first 3 lines are the relevant ones: