Simply adding a gong isn't really supported by dahua.
But there are some options for this if you are willed to "play" with scripts (e.g. on a RPi or NAS). You can ead
this (use g**gle translate).
If not, buy another VTH.
Also cloud services are not really supported (except dahua's own cloud stuff). But as mentioned, there are tons of options to get what you want with scripts. You can try e.g.
this to get MQTT.
There is an open
thread where your question might be answered better. Off course you can start digging reading the options you have in the
DAHUA_HTTP_API.