How to use approval series in case of custom forecast load

in our system, we export/upload forecast generated by Demantra to EBS weekly via a custom export integration workflow.

This workflow runs weekly to export forecast data. We want to implement an approval step before starting the export workflow.

I see that, in export integration interface definition there is an exception section where I can set the condition to export forecast only if "approved by" is not null i.e. the forecast is approved.

We want to implement this logic in our custom system. i.e. we want to create a custom approval series which would populate with user id who last approved the forecast, then based on this the forecast will be exported.