I am not sure what to pass in as the JSON Body to the request though as Swagger or OpenAPI is not showing correctly. It is just displaying the Schema references rather than the actual JSON body.
We are working on a fix. Thanks, for pointing it out.
In the meantime, here is the definition of the TrainingRequest:
If you want to train a combined Rasa model, you need to provide the content of the domain file and the config file in the request. Additionally, the training data should be in the request body. Optionally, you can also specify the output directory and a boolean indicating whether you want to force training or not.