Hi John,
I encountered the same error and just found another discussion here.
  
  
    Hello there, 
Server info: 
1 - I´m running ubuntu server 18.04 
2 - Elk stack running on 7.13 version 
I´m trying to add a fleet server on a self managed host but no luck. Following the kibana instructions this is what I´m getting so far: 
1 - From kibana screen, I´m trying to add the fleet server 
2 - Downloaded the elastic agent to the same elk server (DEB x64 version) 
3 - Generated the token 
4 - Followed the instructions for the commands to be used 
Then, I receive a lot of X509 errors. So…
   
 
As written in the discussion, adding --fleet-server-es-ca addressed the error in my case, too:
sudo ./elastic-agent install -f --fleet-server-es=https://localhost:9200 --fleet-server-es-ca=/usr/local/etc/elastic/elasticsearch-ca.pem --fleet-server-service-token=AAEAA...Mdw
 
I hope this helps!
             
            
               
               
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