Prepayment invoice is not showing invoice in payment form during partial payment

Dear all,

My one prepament invoice is not showing balance amount invoice during payment mode. This is partial payment and we have done partial payment

for other prepayment invoices already. EBS version is R12.1.3 and pay in full checkbox is also disable with invoice status "AVAILABLE", Instead

of Unpaid or Partial Paid. Could any body help me to sort out this issue.

Thanks