conflicts with:
HPD13A and RFM95W are not the same module (but they are compatible).
What is the actual module you have used?
The same 8-bit AVR microcontroller is used on LoRa32u4 and Arduino Pro Mini (although on 3.3V it runs at 8 MHz while on Uno runs at 16 MHz). So you may find relevant information in LoRa32u4 and Pro Mini articles on the forum. See Big LoRa32u4 boards topic and notice the “Get the basics working first” information there.
For getting more memory available you can disable PING and BEACONS to save some memory (see LMIC documentation).
Have you properly configured the LMIC library for the correct region / frequency band?
Check the Data tab in the TTN Console of your Application and for the device to see if you can find any Join requests coming in.
If not then you may not have gateway coverage in your area and/or the LoRaWAN keys / id’s may have been entered incorrectly. See: Format of Keys and ID's for Arduino LMIC libraries [HowTo]
As said by others already. The LoRa module requires 3.3V supply voltage and 3.3V logic levels. Arduino UNO uses 5V for both however. Converting the logic levels requires a level converter.