How can I capture packets on devices with OneShotSenderHelper (signetlabdei / LoRaWAN module) application installed in ns3?

Question

I'm trying to capture and save LoRaWAN packets into a pcap file. But I can't seem to get it to capture the packets. I am very new to ns3 and to the open source LoRaWAN module for ns3.

I want to capture the packets at the gateway.

NS_LOG_INFO("Creating the gateway...");
NodeContainer gateways;
gateways.Create(1);

mobility.Install(gateways);

// Create a netdevice for each gateway
phyHelper.SetDeviceType(LoraPhyHelper::GW);
macHelper.SetDeviceType(LorawanMacHelper::GW);
helper.Install(phyHelper, macHelper, gateways);

/*********************************************
 *  Install applications on the end devices  *
 *********************************************/

OneShotSenderHelper oneShotSenderHelper;
oneShotSenderHelper.SetSendTime(Seconds(2));
oneShotSenderHelper.Install(endDevices);

/******************
 * Set Data Rates *
 ******************/
std::vector<int> sfQuantity(6);
sfQuantity = macHelper.SetSpreadingFactorsUp(endDevices, gateways, channel);

/****************
 *  Simulation  *
 ****************/

Simulator::Stop(Hours(2));
Simulator::Run();
Simulator::Destroy();