Tado radiator thermostaat is not mounting

Efi

Hi,

I just got tado slimme thermostaat v3 + startpakket and it seems that one of the radiator thermostats cannot mount in any of my radiators. although with the other one everything went very easy thanks to your detailed instructions, the other one does not seem to work. I can successfully pair it, but not mount it. Can you please help with that?

Thanks,

Efi