I achieve this by dropping in an ‘Update Profile Property’ action at the end. In a test profile, create a new custom profile property that fits the flow/segment you want to track. Like maybe ‘Finished Post-Purchase’ and then for the value put TRUE.

Then back in your flow, it should now show that field as an option for the update action. Plug it in the details and update that new property to TRUE in the action (or whatever value you’d like!)

Then craft a new segment to track all contacts that have the profile field filled in. You’ll then have a segment of contacts who reached the end of your flow.

Hope that helps!