Guys, I have found how to solve the Mirror function not working stating that you have 0 activations. It is not needed to put any file anywhere.
I have two phones (LG G4 and Huawey Nexus 6P), both on Marshmallow (6.0.1) and both work perfectly fine with the 3.4.X version of the Easy connected app. Using USB or WiFi connection.
The only needed action is to uninstall the old server app FROM YOUR PHONE.
If you have ever tried the old (or even a newer version) of the easy connected app to connect your phone, it installs two apps in your phone. An "easy connected server" app and a Drive Mode App(or something in Chinese letters).
The drive mode is just a stupid app that is supposed to have a car interface, you can safely unninstall it after it is installed. The server App is the one that is very important. It is the one responsible for sending the screen information from the phone to the HU, and also to receive the touch information from the HU.
The old server version installed on your phone is the one giving you trouble. And it is giving these certificate errors.
Whenever you are trying to install a new version of the EasyConnected app, remember to uninstall the old version of the server app (on your phone) and then restart the process.
If I had this info earlier, it would save me a lot of trouble.
The server App does not appear in the normal App drawer, you have to go to:
Settings->Applications->all installed to find it. Simply click it and choose to uninstall. (Easy Connected Server)
After that, restart the process to connect your phone again (remember, the first time you have to use the USB connnection) and it will be installed again. It even auto-update itself after installation.
Also remember that you have to have USB debbuging (under developer options) active all the time.
Sorry for the long post, but I wanted to give you all the info necessary. I'll also let some words below so people can find this post in search.
EasyConnected, Easy connected, Mirror function, mirroring, display
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