First step - on the command line do a “cmk -D hostname” to get the agent command executed by CMK.
Try this command manually and inspect if there is a little bit more error message.
Most times you can run the agent with debug or verbose output to get more information.
I have executed the command and I get the same error
OMD[cmk_atcan]:~$ cmk -d server.domain.net
ERROR [special_storeonce]: Agent exited with code 1: Connection error: HTTPSConnectionPool(host=‘server.domain.net’, port=443): Max retries exceeded with url: /storeonceservices/cluster/ (Caused by NewConnectionError(’<urllib3.connection.VerifiedHTTPSConnection object at 0x7efe58635f90>: Failed to establish a new connection: [Errno 111] Connection refused’,))(!!)
Capital D
As the storeonce special agent has no debug option you need to insert a little bit debug code by yourself if you what to find out what happens. I think that you have only two options whats wrong on your system. There is no data under “/storeonceservices/cluster” or the user you use has no rights.
For the first problem it is important what software version your storeonce is using.
v4 ?