How to create a custom event in rules?
Let's assume that the Rules action that you want to trigger is to just set a Drupal message like "Rules action related to payment confirmation". But this action should only be triggered when "Viewing the content" located at your confirmation page, which has a path like "/payment-confirmation".

To get this to work, use the rule below (in Rules export format, just import it in your site and check the results of it):

{ "rules_extra_action_about_payment_confirmation" : {
    "LABEL" : "Extra action about payment confirmation",
    "PLUGIN" : "reaction rule",
    "OWNER" : "rules",
    "REQUIRES" : [ "rules" ],
    "ON" : { "node_view" : [] },
    "IF" : [
      { "data_is" : { "data" : [ "site:current-page:path" ], "value" : "/payment-confirmation" } }
    ],
    "DO" : [ { "drupal_message" : { "message" : "Rules action related to payment confirmation" } } ]
  }
}


The rule above should be close to what you're looking for, except from these further refinements:


Replace the rules Action by your own rules "action" (which you didn't specify).
If you want your Rules Action to be performed before your confirmation page is actually shown, then replace the Rules Event (= "ON" : { "node_view" : [] },) with "ON" : { "init" : [] }, (= "Drupal is initializing").