In many cultures, people have the tradition to say hi or hello before they start a conversation. And this will be considered part of polite and use to show your manner, but in China, we don’t really do this in WeChat.
Because whoever received the words “Hello” will be very nervous. In China we have an unwritten rule when you asking someone “Are you there” it means you need their’s help. And basically, that will be a tough request, like you need money.
So every time, when I see a messenger say nothing but just “Hi” or “What are you doing”, the first thought comes up in my mind is, he/she must want something from me. And, yes, the stories always end in this way. If you just wanna have a chat with your friend, don’t start with a “Hi”, it will also be considered as bored starting.
But I never said you shouldn’t use these words, but after this please clarify yourself. Like, “Hi. What are you doing, I am thinking maybe we can have a dinner together.” This is literally better than “Hi” and wait for their reactions.
Also, you can ask your question or send a request directly. Like when I enter a cafe in Ukraine, I said Latte and my friend tell me this is impolite in Ukraine. I guess every country has their own culture, and there will be no harm to do as the Romans do.