1. Create an API token for the monitoring user. Important note: for security reasons, it is recommended to create a separate user (Datacenter - Permissions).

This could be clearer. 
  Step 1. Create an API user.
  Step 2. Set permissions . . . 

Please provide the necessary access levels for both the User and the Token:

• Check: ["perm","/",["Sys.Audit"]]
• Check: ["perm","/storage",["Datastore.Audit"]]
• Check: ["perm","/vms",["VM.Audit"]]

There is no way to set permissions on the token. I spent at least an hour trying to figure out how to do this. It cannot be done and what's more, it doesn't NEED to be done! 

Further down the page the author doesn't make it clear whether we're working on the proxmox server or the zabbix server.