Ash,

I assume you mean Medius Flow XI when you talk about XI. And when you mention ECC, I assume that you are talking about ecc.de (European Commodity Clearing )

Am I correct?

Then I do not understand your first statement when you say "My Client want to start UBL Invoice for customers"  because that implies OUTGOING invoices from your clients system to that of their customers. But the systems/enties that you mention are more related to Receiving invoice.

So I hope you can give use some more details ...

Kees D. 

You do not mention what "XI" and "ECC" are, but I will assume they are a software application of some sort.  Maybe another ubl.xml.org visitor can answer specific to that brand of software.

In general, your task to integrate a UBL invoice into any brand of software is to identify which components of the XML are to be mapped to the components of your software. 

An XML processor under your control then walks through the content and you populate your software as you encounter the content in the XML. Alternatively, if your software accepts XML input of another vocabulary, then you simply transform the UBL XML into your application's XML and then your application can ingest the content without any software changes.

To review the possible content of a UBL Invoice, you can review the "Summary Report" linked from the invoice documentation at http://docs.oasis-open.org/ubl/os-UBL-2.1/UBL-2.1.html#T-INVOICE

It is also good practice to validate your incoming UBL instance against the invoice schema (also found at the link above) before doing your ingesting so that you know you are working with consistent data.  You may also wish to validate the instance against any value constraints you have on the content.

I hope this helps.

. . . . . . Ken