Hi
Adding to Anil;s comment, you must activate CVI (Customer vendor intergration) to TRM, effectively integrating the Business partner. By standard, TRM can be integrated to customer subledger, however, you could look at the user exi/enhancement with vendor subledger.
Also you would need to add a certain configuration around update type to allow the subledger posting.
There are lots of threads available in SCN in this treasury forum on subledger integration with TRM. Please search.
Hope that this helps
Taro