Hi @Matthew1,
please check you configuration of the host inside wato. You need to disable to check the agent too, beside of snmp.
to be a bit more informative:
At the service Check_MK inside the brackets [] you can see the data source programs used to monitor the host. You are monitoring your host via agent and SNMP, but your host only supports SNMP. You can tell checkmk not to try to ask the agent (where the connection refused come from)