Problems with installation

I have bought 4 new weather stations. They are impossible to connect. Always a faullt occured try again later. I have scanned the qr code at the indoor module, placed the batteries for the outdoour correctly and have power, but there alwys comes try again later when the app says it is seearching the device. Internet router is comnnected and visible in the app. What to do? I am irritated because I can not monitor the temperature in my houses.