@Russ The problem was not the paths. It turned out that smartthings-cli wanted a fresh login by root.
I tried logging in to GUI with root, but was unable to initiate the login prcess that way.
But typing --token <uuid> after each command did the trick!
(<uuid> being the token from https://account.smartthings.com/tokens)

Cron and other services that start at boot are still unable to run the commands.
Now I get "Error: did not get any data from stdin".

I bypassed the problem by running a python script manually. This script stays open and executes the smartthings commands as needed. The downside is that if the power goes out and RasPi reboots the script does not run automatically.

This is a very powerful tool. Just started making my own automations with it in a Linux environment (Raspberry Pi).

I am putting my commands in bash scripts and bashing them in with other tools.

However some commands, like

./smarthings devices

will only run manually from the command line and will not work with sudo. In case I run it as root with sudo I get a "logging in..." message and it's just stuck there before i hit cntr-c. Also user level cron will not run this command.

While

sudo ./smartthings --version

executes with no problem and can be executed in crontab also.

I think it is a problem with permissions, but i cannot figure it out.
Any help would be much appreciated!