Heltec’s ESP32_LoRaWAN library is proprietary. Essential parts of the source code are not public, not open source and its use is limited to Heltec ESP32 boards. You will therefore not find much support for it on this forum. Many prefer to use non-proprietary open source software instead.
See the tips and instructions in the topic start.
It will be easier to start with the library and examples mentioned there.
Those examples provide the basics to get a LoRa board working with TTN and will be easier to get support for on the forum.
The MCCI LMIC library currently is the standard LoRaWAN library to use with the Arduino framework.
It is open source, well-documented, well-maintained and different from Heltec’s library, it is not limited to a single microcontroller (family) and not limited to boards from one specific manufacturer.
Also see: Overview of LoRaWAN Libraries
LoRaMac-node is a LoRaWAN reference library created by Semtech. It does not support the Arduino framework however. Both LoRaMac-node and the Arduino framework are open source.
Heltec has ported LoRaMac-node to the Arduino framework but they have made their port proprietary. Heltec does not provide essential parts of the source code and their library can only be used with Heltec ESP32 boards.
Heltec has taken from the open source community to benefit their products, but does not contribute back to the community. Instead they have made their port closed source and proprietary instead. This is poor practice and conflicts with the mindset and mentality of the open source and Arduino communities.
As a result Heltec’s ESP32_LoRaWAN library will only be used and tested by a limited number of users.