That API doesn’t look like REST level 3 API. For example, there’s an endpoint to create a node. It is not referenced by root or anywhere else. GetNode endpoint does include some traversal links in response, but those links are part of domain model, not part of the protocol. HAL does offer a protocol by which you enhance your domain model with links with semantics and additional resources.
these levels? https://blog.restcase.com/4-maturity-levels-of-rest-api-desi...
I'm not saying it's perfect, but it's really good, and you could create a client for it in an evening.