Read the Dahua HTTP API..
This functions don't send one reply... it halts HTTP connection indefinitely and sends many replies encoded as multipart in the same reply (it don't close connection)..
You can't use/display URL to this function simply in web browser - You need to write proper code in python or java-script to support receiving data from this function.
there are extra parameters to define keep-alive data which server/client will send every x seconds...
On GitHub You will find many apps / modules that are using this call:
You can browse theirs code..
PS. You didn't wrote for what You need receive events, but there are read-to-use Dahua modules for Home-Assistant, HomeKit or Frigate..