Unable to implement export to CSV / Excel

In the world of Radzen, the interface would happily generate the code and buttons needed for export to Excel/CSV This does not appear to be an option in Blazor Studio, which is a real shame - as these options are a great time saver. Anyway, I have dutifully followed the available documentation and am now faced with an error of the form:

I can see that the HttpGet is defined in the generated export controller. However, I am clearly missing something - any advice?

Many thanks.

Enabling export is easy. Just check the corresponding option when generating CRUD pages: