Question about Voltcraft SEM6000 CH

Hello everyone, I have owned two of these Voltcraft devices for a few days now. Unfortunately, I have not yet been able to establish a connection with the smartphone (including restarting the smartphone and activating location services). I have tried it on another Android device as well as on an iPhone, but none of these devices are recognised. Strangely, one of the Voltcraft devices flashes green at first and then changes to a flashing blue. The other device lights up green, switches on and off occasionally, and then doesn't light up at all. When I press the button on the device, it does not switch audibly like the first device does. Can anyone help me? Many thanks in advance for your support.