AWS SSO with Amazon Managed Grafana not working (redirection to NULL)

Hello here,

We have enabled AWS SSO with a delegation of IdP management to Azure AD, which is working fine.

We are using Amazon Managed Grafana, and use AWS SSO to assign users: working fine too.

The problem is we can't use the URL application in the AWS SSO login page to reach the AMGrafana dashboard. When we click the shortcut from the SSO (when you get to pick an account or an app), we get a saml URL which redirects us to a https://null/login

We didn't see anything that we could configure so to fix the issue, and directly lands on AMGrafana from the AWS SSO login page as intended.

What did we miss?

Thank you for your help.

Kind regards