problem pair device

[lejibxl]

the installation on the HA side went very well thanks to the explanations, the MQTT is well active on the port 2001 and it is possible to connect to it via an MQTT client W/ parameters.
On the GSM side, the application sees my device (MSS310 with the last FW) but in the "pairing" process it blocks every time (see screenshot).
the message in French is "a problem has occurred. The application has cancelled the request to select a device".

As it is much more difficult to debug on the mobile side, I don't really see where it blocks.