When creating multiple items in 1 call, the client still defines the return type as CollectionItem when in reality the return type is {items: CollectionItem[]}.
Honestly, for a company that is shutting down their v1 API, your v2 tooling and documentation is inconsistent and at times incorrect. There are calls where the tooling enforces a type but the API rejects this type, and when trying to satisfy the API validation, the tool then enforces the wrong type back. This is a mess and I am surprised a company as big as webflow has such big gaps in their tech and tooling. Have you not tested these things internally?