SUM function only accepts column reference as an Argument

Hi There,

I have two columns in two differnet Tables

Table 1 : Analysis   &  Column Name : Missed Revenue

Table 2 : Billing  & Column Name : Revenue

I want a Card to hold the percentage of 'Missed Revenue/Revenue'

I tried to create a measure to solve this :

Measure = sum(Analysis[Underbilled Cost]/sum(Billing[Revenue]))

but am getting error as ' SUM function only accepts column reference as an Argument '.

Alternatively, if this is wrong approach can anyone please direct me to how to solve this aother way.

Thanks,

AB