@laix 

Please try this firmware:

http://static.tp-link.com/MR6400_voip_beta_2016-09-06_15.01.35_1474602142560j.zip

@Tony 

I just tried but the file "router.bin" doesn't work,

Is there another way to update the MR6400  firmaware?

I go into firmware upgrade and insert the file "router.bin" after unpacking the file .zip

It creates a folder with many file...

@laix 

There should be one bin file that you upload to the router. What message do you get when you try to upload it?

@Tony 

When I unpack the beta firmware I get this

When I use the router.bin file to update the firmware on the router I get this

@laix 

What is happening is that you are extracting the .bin file. only extract the .zip, not the .bin. If you extract the .bin file, then you get the files you are looking at.

So download the .zip file, and only extract that, nothing else.

@Tony 

thanks, I used an unzip software which worked weird way.

Change software, everything works!