Does the transmitter code loop reporting successful transmits?
How far apart are the two units?
UWB is fairly hard to see on a spectrum analyser, the legal maximum transmit power is 1 mW (0 dBm) but the maximum average power over any 1 ms time period is under 0.1 uW (-41.3 dBm). Unless you have reasonable equipment and know exactly what you’re looking for it’s very easy to miss it on a spectrum plot, it’s not like most signals where there is a nice clear carrier to look for.
Assuming the startup code is working and reporting sensible device ID information then the physical setup is probably OK. I’m not familiar with the hardware or drivers you’re using so other than general advice like checking the receive interrupt pin or periodically polling the device status register on the receive side to check what it’s doing I can’t really offer much advice.
A lot of arduino libraries require you to call a polling or background function as part of your loop() code, is that the case for this one?