Login to Opsgenie at https://app.opsgenie.com or https://app.eu.opsgenie.com (if you have an account in the european union)
Make sure you already have a team, if not follow this guide https://docs.opsgenie.com/docs/teams
Click "Teams" in the Menu on the left
Select the team that you want to notify
In the teams configuration menu select "Integrations"
click "Add Integration" in the top right corner
Select "API" integration
Give your integration a name, copy the "API key" and safe it somewhere for later
Make sure the checkboxes for "Create and Update Access" and "enable" are selected, disable the other checkboxes to remove unnecessary permissions
Click "Safe Integration" at the bottom
Check your browser for the correct server apiURL. If it is "app.opsgenie.com" then use the us/international api url api.opsgenie.com in the next step, otherwise use api.eu.opsgenie.com (european api).
You are finished with configuring opsgenie. Now you need to configure argocd-notifications. Use the apiUrl, the team name and the apiKey to configure the opsgenie integration in the argocd-notifications-secret secret.