Howto communicate multiple LoRa

Hello I’m new with LoRa, I have some trouble with communicate my SX1278 with arduino. in my case i have 3 nodes LoRa and 1 receiver there nodes are sending data serially until the last node send to the receiver. i try with the example code on arduino (LoRa Duplex) but the LoRa always give me a notice yhey the lenght that receive not match. anyone can help me?? i use arduino mega for each node and receiver. thank you so much for helpp!!!