Shipa,
this error is standard,
error is not genreted becz of BAPI.
when you pass GL number to BAPI check GL number with leading zero available or not.
if not convert to proper GL format using
CALL FUNCTION 'CONVERSION_EXIT_ALPHA_INPUT'
EXPORTING
input = wa_bapi_gl-gl_account
IMPORTING
output = wa_bapi_gl-gl_account.
and then pass to BAPI.
also
check with functional whether your taking correct ref. COA & GL.
whether this GL is relevant this COA.
Regards,
Sandeep