"Azure Services discovery failed for subscription <subscriptionID>. Invalid Application key" - Error message upon editing a New Azure monitor using Azure Organizational Account mode
Troubleshooting:
In Azure Organizational Account mode, Applications Manager internally generates the keys ClientID, TenantID & Application Key. After 1 year of creating it, the Application Key expires and throws the above-mentioned error message.
In this case, the user has to log in to Azure portal, go to 'Azure Active Directory' -> App registrations -> Select 'All apps' -> Click on the application starting as "ApplicationsManager-<YourSubscriptionID>" -> Settings -> Keys -> Delete the expired key -> Create a new one by giving 'Never expires' -> the key will be displayed upon saving -> Copy the key and update the same in the "Application key" field of AD Application & Service Principal mode and update.