Wrong max voltage settings from Dual R3

I have a Sonoff Dual R3.
Afyer added to my account the Dual R3 I tried to settings OPS.
I selected Max Voltage and I wanted to set 250V, every time I saved was displayed “Failed to save’.
If I setted 240-240, in first step saved but the second step failed to save.
In my home the min voltage si more then 240V.
If I set Max Voltage 2400 the message was " Max voltage is 300V”.
I contacted Sonoff support 2 weeks ago but until now I have not received a response.
Have you encountered this problem before?