Thingsboard integration

I find in the manual to add a payload codec. So the received payload is base64 coded. Am I right that the script has to decode the base64 into my original payload? My original payload is JSON formated.
If I am right, where can I find an example how to add a working payload codec?

With LoRaWAN, the payload sent by the device is a binay blob. This blob could be anything, maybe in your case JSON. The codec function receives this binary blob as a byte array and it is up to your function to turn this back into the original data (e.g. JSON). Please note that sending JSON over LoRaWAN is not recommended as it adds quite some overhead in terms of payload size.