I am studying materials related to FCM Messenger Web push notification. While I came across a streaming message and an upstream message, it is obvious that the HTTP server only allows incoming messages, while the XMPP server allows upstream messages.
It’s hard for me to understand the difference between the “downstream” and “upstream” messages, and the details are not well described in FCM. I tried to search the Internet, but I had no luck. Please help me as I am new to coding.
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