Complex JSON from a REST Api with Dataflow

Hi.

I have a Rest API that retreives a complex json. In order to flatten that. Do i have to store de json in a file first? or can i flateen that json from the Rest API directly?

Do you know if is it an examle? (i found videos of flatten complex json from a json file, but not directly from a Rest API)

I get this error trying test connection

This api works properly in a copy_data task

Thank you