Press enter key to receive http request

I have a problem with Flask. My code is running on a server, and it has the purpose of process http request made from an app built with Flutter. It works, but sometimes I have to press the enter key in the command line to process the request: I tried to add “\n” at the end of the url and it works for GET requests (I think this was the solution), but for POST it doesn’t work.

This is the method that should execute when a new POST request is received:

@app.route('/proveedores/agregar', methods = ['POST']) 
def proveedorAgre():
    content = request.json

But sometimes the function doesn’t execute unless I press enter key in the cmd

Someone know what is happening? Thanks in advance!