Straightforward letters of credit (6)
I believe the answer is:
'straightforward' is the definition.
(straightforward can mean direct)
'letters of credit' is the wordplay.
'letters of' indicates an anagram.
'credit' is an anagram of 'DIRECT'.
(Other definitions for direct that I've seen before include "Show where to go - straight" , "Straight, without diversion" , "Organise; straight" , "'Straight, without deviation (6)'" , "Take charge, of a company or film say" .)