Hello, Santiago.
There is a proble of empy Flow type fields if you have 2 or more Flow types.
Use BADI FTR_TR_GENERIC, method EVT_APPLICATION_START
Sample code:
" Limit this code to specific product type where you have 2 flow types for IF pi_proxy_transaction->a_transaction-sgsart = '51A'. " We use field-symbol to enter our screen field, " becuase we are not able to update field directly. FIELD-SYMBOLS: <fs_mseg> TYPE ANY. ASSIGN ('(SAPLTM00)VTMHPTBWG-SFHAZBA') TO <fs_mseg>. " Always check if field-symbol is assigned to our field IF sy-subrc = 0. " Assign Flow type to screen field <fs_mseg> = '1100'. ENDIF. ENDIF.