How can I create a historical overview from a flexfield CHARACTER Data type?

I have data information stored in a CHARACTER data type flexfield.

To expose it in an analysis in Oracle Business Intelligence (OITBI), I navigate to the 'Incentive Compensation Subject Area,' then select 'Source Transaction Details' to access the flexfield from the list.

The result is the flexfield that has been uploaded, and it is filtered by the period defined in the prompt.

My objective is to retrieve information from this flexfield for the previous period while remaining within the same analysis.

However, when I attempt to use the 'Time Series Calculation' function, specifically 'AGO,' I encounter the following error: