Dear Imran and Anastasia,
In order to generate outgoing payment files in ISO 20022 XML pain.001.001.03 CGI V3 format, you will need to download a DMEE tree called CGI_XML_CT, and assign it to your payment method in FBZP in SAP. There are a number of prerequisite SAP Notes and system settings which can be read in SAP Note 1665873 CGI: DMEE XML Format as per ISO20022. This SAP Note also a very useful step-by-step guide (attachment CGI_XML_CT_IMG.zip) as well as the actual DMEE template (attachment CGI_XML_CT.zip). Note that the Standard SAP DMEE CGI_XML_CT does not cover all country requirements. So, depending on the country for which you are making the payments, you may need to tweak that DMEE using Transaction DMEE in SAP.
Some banks, like Citi, JP Morgan and HSBC have developed their own ISO20022 templates (called "integrators" or "adapters") which can be imported into SAP via Transport Request. This would accelerate your ISO 20022 XML project. May I ask which bank are you dealing with, and for which countries do you need to make the payments for? In SAP OSS, search using the Search Term CGI_XML_CT and you will see a lot of SAP Notes giving the latest update and guidance from SAP in this area. I've been working with ISO 20022 XML pain.001.001.03 CGI V2 & V3 formats in EMEA and APAC for the last 6 years, and am happy to help if you are stuck.
Regards, Garoid Pierse.