Sensor not detected by modem

I just purchased a second sensor (sku PR55-1PC) and for a unknow reason it can’t tramsit data to our modem (Industrial IoT Wireless to USB Modem).
I already have a sensor (same sku) which can transmit but the second is not…
To make my test I use AlphaStation, but only one sensor is detect.
How can I fix that problem ?

In the first order, you purchased the devices with 2.4ghz radio modules; in the second order, you purchased 900mhz.
This won’t work.
You need to have the same radio frequency across all devices.
I will recommend sending the 2nd unit back, and we will build it with 2.4ghz radio

Okay… My mistake. I’ll return back the second unit…

Thanks for your quick answer!