I have done this many many times. The best suggestion is to check in in the app and use the chat feature to inform them. Only if they do not respond in the chat do you need to call them. Sometimes they are slow, but I have never had to call them.

If you feel a bit insecure take a screenshot of the chat showing that they confirmed your plans. I have never needed this, but if they were to cancel your night, then the chat history would also disappear. This way you could show them and prove that they had agreed to it - that makes it their problem to figure out how to reinstate your booking.