As a brief note, this is probably not the best list for this. You would do better to ask questions like this on -general where you have more application developers and so forth. This is more of an SQL question so asking people who are hacking the codebase may not be the best way to get it answered.
Also, it is Postgres or PostgreSQL. People will assume you are totally new if you call it Postgre.
but it's throwing an error as : 0 SQLState: 42P01 Message: ERROR: relation "l_inv_lines" does not exist
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Thanks & Regards, Brahmeswara Rao J.
When you ask on -general, please include the query which is actually causing the problem. My guess is that either you didn't declare the type properly or there is some other error in your function, but the information provided is not sufficient to answer it.