So, basically, there are two devices (Elastel eg500, which is basically Raspberry Pi 4). When I am using one device as sender and another as receiver, & using the below code, it is working just fine. Here, the situation is, sender will continuously wait for receiving dta from a radar device using RS-232 communication. When sender receives the data, it will flash its own LEDs & then send a packet to receiver device via LoRaWAN communication. So, the receiver is waiting continuously for receiving LoRa packet. When it receives a packet, it flashes its own LEDs for flash duration period of time.