Here’s an example I did awhile back that uses a parameter with the export mapping.
https://modelshare.mendix.com/models/7976af12-8664-49b4-8d83-aa6839e25d5f/example-getapi
im using the export mapping to generate a json string. Hope this helps
In the ExportMapping doubleclick the entity to get the popup "map entity '<x>' to schema obhect element '<y>'" and on the line of your Schema Value element you can select any Entity attribute having the type need and select a microflow that you can use to create any logic you want to get the result you need.
Thanks, but this is not working. I tried it.