Summary:

With no seats available for current subscription level when a new user logs in to Atlassian account, SSO login fails with Opsgenie and users will be redirected to Opsgenie login page without any clear notification. 

Steps to reproduce

• Consider the current Opsgenie plan is for 6 users
• Invite a new user to the site with Opsgenie permissions
• User tries to login to Opsgenie url  https://<site-url>atlassian-app.opsgenie.com 
• User gets redirected to https:/id.atlassian.com for SSO login
• After authentication, user is redirected to https://<site-name>.app.opsgenie.com/auth/login?type=sso&failed=true with no other error messages

This makes a wrong impression that there is some SSO login issue, whereas the real issue is with the subscription

Suggested Solution:

• Include an error message which mentions the real problem which is the exceeded user tier.
  Ex : Your organization is out of seats please contact your admin.