Had you tried it manually with the transaction what you want do with the BAPI?
Does it work manually, or not?
If it works manually, then you probably did something wrong with the BAPI.
But if it does not work in the normal transaction either, then you do not need to search for error in the BAPI
Is that clearer?
I further said that you did not care about your other question, It is still open, you got a question and never replied. If the problem is solved then tell how and close the question.