Transport Reason Code can be passed along with miles in the MILES field.
Miles field is in the Charge master; see Image 1.
For eg: if Miles is 33 and Transport Reason Code is D, then in the miles field we have to enter 33D.
System will parse this and show the Transport reason code.
If the MILES field has only miles without any Transport Reason Code, system by default picks up the Transport Reason Code as “A”.