Is it possible to define an extra payload fields directly from TTN application different per device like an API Key

[arjanvanb (Arjan)]

In July 2017, @htdvisser wrote:

@htdvisser

You can add “attributes” to your device with ttnctl. This functionality will be added to the console too.

For TTN Console, maybe it’s on the roadmap for version 3? Also, I don’t know if you get these attributes in the MQTT message. You surely won’t get them in the Payload Format functions.

See also the other replies in that topic. And maybe related: How to best write an application that contains many nodes with different measure data types.