How to train the rasa providing json in http API instead of yaml file in rasa version < 3?

I want to use rasa nlu to identify the intents and entities. I have my UI for the chatbot. However, I am not sure the best approach to implement with rasa. Should I use rasa nlu or go with rasa-x as it has more structured APIs, exp: Training API for rasa-x we can send the data in JSON format in the opposite rasa nlu needs data in YAML format.

You should use the Rasa OSS yaml format.