The app was registered and worked fine to call O365 Discovery Service to discover API endpoints. But it stopped working lately. I know Discovery Service is to be obsoleted next year, but it should still work now.
Error is:
{
"error": {
"code": "101, Microsoft.Online.Services.O365Discovery.O365DiscoveryException",
"message": "The app ID is blocked for access of the O365 Discovery Service."
}
}