Today I have upgraded to the Nextcloud 13!
Everything went very well!
I went to the apps and saw the Talk app and i installed it by pressing the button!
It’s so easy ?!? 
After that, I downloaded the “Nextcloud Talk” app on a smartphone android and on an Apple .
In Apple’s smartphone seems work well ( for example in contacts I see users who are in my Nextcloud )!
But, in android smartphone doesn’t work. Once I put my credentials, I get the following image:
Why is this happening ?
Thank you! 