Partial Payments not allowing in FPCJ

Hi Experts,

I have a requirement user wants to accept partial payments from customers through FPCJ cash Desk but there are two conditions in FPL9 having ABC Line items and XYZ line items.system has to be look into first ABC line items if there is no single penny then only look into XYZ Items.

ABC Line items belongs to current execute Company

A001-0010/0020....RS.010

A002-0010/0020....Rs.030

A003-0010/0020....Rs.060

XYZ Line items: Current company need to be collect from Customers and remitted to other company.

Z001-0010/0020....Rs.100

Z002-0010/0020....Rs.050

Z003-0010/0020....Rs.020

In connection with above scenario, User wants to enter in FPCJ- Co.code,BP and Payment then after making posting, during this time system need to select first ABC, if total open item not matching with FPCJ entered Payment system need to through a error. How to over come this help me.

Clearing Steps which i am using for Cash desk payments

Thanks,

Abbas