Pass internal table to workflow container

We have written a coding on the method to calculate the Ageing (which is dynamic). and the same is stored in it_gpdata. We want the data in this to be passed to method name Ageing. The parameter used is ZAGE & the coding for calculating zage is written in this parameter. When testing the BO, we are not getting the values in 'Ageing' method. We have maintained multiline in the parameter. Still we are not getting. Please guide.