Hi Sandeep,
Could you please elaborate on the exact expression you're using?
InStr can work for a character placed anywhere in the string, it doesn't necessarily have to be in the first position. so if there are orders with 'P' anywhere in the entire string it will be considered as a pass.
If you are looking to process only the orders that start with a 'T' and not with 'P' you might want to consider LEFT substring expression to get the first letter using - Left([stringT], 1) where stringT is your Order name and then check if the result is a P or T.
Hope this helps.