Difference between Rasa Open Source and Rasa X Post Message HTTP API

Hi, so in Rasa Open Source there is an API to post a message to a conversation and it should not trigger the prediction loop. Rasa X somehow has the same endpoint but this one will trigger the prediction loop and give an actual answer. However that’s the behavior I get when I am calling my Rasa X backend. Is there any way to call the Rasa Open Source API in my installed Rasa X setup? Afterwards I would like to predict the next actions and add the according events by myself.