Error sending json to server. How to fix?

Question

MongoDB

Error: UnhandledPromiseRejectionWarning: Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client

This happens when json is sent from Postman to the node.js server.
At the same time, data is entered into the MongoDB database

How to get rid of the error? I don't even understand its meaning.

Answer 1

And why on line 23 res.send?
You then send the response through res.json();
Apparently, res.json sets the headers for the response, that json is stored there. And since the answer has already been sent, there is a problem with this.
In general, the error says that you have a promise somewhere without a catch block, I suspect that this line 23 is the problem.