Message issue, cannot activate text forwarding

[icymountain]

Hi,

I am using an MPB with macOS Sierra, and was trying to get text forwarding to work on it, so as to synch my messages with my iPhone. In fact, it used to work, but it seemed not to work anymore, so I deactivated this device from my iPhone (others are still ok), and tried to re-activate. When I select my device from the iPhone, Messages starts on the laptop, but the activation code does not show anywhere. I checked with another device, and know where the code should show up, but there is just no code that appears.
What should I do ?

(I tried to ask the question on the Apple communities website, but it does not let me post there as it says I am not allowed to do so... strange, I am connected, with my login...).

 

[icymountain]

Update: I now have the issue with another of my devices.

1. iMessage stopped synching.
2. I decided to remove the device from the list of devices to which messages should be forwarded (on my iPhone), and to add it again.
3. When I add it again, the activation code is sent, Messages seems to try to do something on the computer, but does not display the bloody code, so I am stuck, without any forwarding.

Help...