Could you please tell me what is your recommended library for using with HELTEC devices?
In terms of reliability, examples, etc…
IBM LMIC framework
MCCI Arduino LoRaWAN
MCII LoRaWAN LMIC
or
should I install
lnlp/LMIC-node
Should I use platformio or ARDUINO IDE?
PS. We will have many heltec devices with many sensors each one, and reporting data to multitech gateway.
Which ones? They have several different ones with different requirements.
LoRaWAN devices don’t report to a gateway. They report to a LoRaWAN network server. Some gateways have an LNS integrated, MultiTech has those, however those use cases are not the subject of this forum, this is the TTN forum.
And if you plan to use many devices you are probably making money on your offering so you should use a commercial instance of TTI, not the community network where TTI foots the bill.
What type of sensors ?
Perhaps describe the actual application to the forum, using ‘many’ sensors on each node, as you have suggested, could have a significant affect on how you set it all up.
Have you searched ( 
) the forum - there is a whole section dedicated to Heltec devices …
What is it about Heltec? And what do they recommend on their forum?
When was the last update for IBM?
MCCI Arduino LoRaWAN is a wrapper to make using MCCI Arduino-LMIC easier to use
Trace back MCCI Arduino-LMIC and you’ll find it is based on IBM
LMIC-node is a wrapper for Arduino-LMIC that use on PlatformIO - so not installed as such, unless you consider the others to be installed too
And Heltec have their own LoRaWAN code base as well.
If you are doing “lots” of devices with “lots” of sensors, perhaps you should take time out to explore the options - including hardware.
Heltec WiFi LoRa 32 (V2) devices, and each device will have temperature sensor, humidity sensor, CO2 sensor.
And yes, we halve already connected the multitech gateaway to TTN.
Heltec WiFi LoRa 32 (V2) devices, and each device will have temperature sensor, humidity sensor, CO2 sensor., we think we could install 30 devices around our campus.
Last update for IBM LMIC framework was on Octuber 2020.
We think we will use 30 devices (HELTEC WiFi LoRa 32 (V2) around our campus, each device will have temp sensor, humidity sensor, CO2 sensor, and probably a RELAY to be controlled.
Which one library should we use?
The repetition of the same info is just signal noise, you can see how the topic is threaded, we can see all the replies, please stop.
What is wrong with the Heltec firmware?