I can definitely help you create transfer nodes programmatically via the Retell API!
Based on the API behavior you've seen, the node type for transfer calls is likely "transfer_call" or "call_transfer", and you'll need to include a phone_number field in the payload even though it's not returned in GET requests.
I'd be happy to help you get this working properly. Would you like to discuss this in more detail privately? I can provide you with the exact API structure and help implement this for your use case.