Outstanding amount against total collection received

Dear Experts,

We are getting the Collection using 0FIAR_C03, and Billing Information from the 2LIS_13_VDITM. In our logic we need to combine these two data sources/InfoProviders to get the FKDAT(VBRK Table) from 2LIS_13_VDITM into 0FIAR_C03. We have identified VBELN is common field for 2LIS_13_VDITM, 0FIAR_C03(BSID-VBELN).But if i use InfoSet for the 2LIS_13_VDITM(By creating DSO to this Data Source) & 0FIAR_C03, I am not getting the desired result.

How to combine the above 2 things to get the FKDAT.

Best Regards,

Venkat P