I have a server-side app (written in C#) that creates a call between a JavaScript client and an external phone number. What I’m trying to do is, in response to a server-side event (which can happen at any time), I need to generate DTMF tones on the active call. Note that this is not in response to any Twilio-generated event – it’s something that I need to do at potentially any time during the call – so I can’t just add additional ‘play’ data to my response to any incoming event.