Data Action schema validation fails for nested objects in multi-org app

Is it possible to pass nested JSON objects through a custom Data Action without triggering a schema validation error in a multi-tenant AppFoundry environment?

“Custom Data Actions support only flat key-value pairs for input parameters to ensure security and performance.”

We are hitting a 400 Bad Request on the POST endpoint when our integration attempts to pass a complex object structure from Architect. The documentation implies flat structures only, but the error response does not specify which field is causing the rejection.