Error 400 is commonly caused by using a module name in prometheus.yml that isn't defined in snmp.yml.

Check the module name in snmp.yml for what you want prometheus to scrape, and update prometheus.yml to use the correct module name.

You currently have prometheus.yml saying to monitor using module "if_mib". Can't see your full snmp.yml, but what I do see shows that you have a module named "apcups" defined. You just have to copy the correct module name that you defined for your Cisco stuff out of your snmp.yml and replace "if_mib" in your prmetheus.yml file with that value, and then restart prometheus.