I can't and my desktop device on "my devices".

Hi, everyone. I need some help. 

I already have the multi device subscription, so I have 3 slots to set my devices on my account. But I've been trying to do so and I simply can't. I followed already all the steps that I should do and they are pretty simple: just login into a new device and it will be added automatically as a new device on your account. On my mobile device it successfully happened, but nothing happens when I try to do the same on my desktop app. I'm asking for help because I don't know what else I can do.

Thank you so much so far.

Best regards, Franckllin.