How to debug this:

kotlinx.serialization.json.JsonParsingException: Invalid JSON at 1221: Expected '[, kind: kotlinx.serialization.UnionKind$POLYMORPHIC@1e6d1014'

This happens because parser was expecting array of [typeName, object] for polymorphic deserialization

How could I know why it was expecting that?

you have something that takes alist of objects but it cannot be sure which classes are serializable.. there might be multiples

Thanks I think I figured it out