I've been able to access this LUIS instance before as recently as last week. Now when I navigate to it I get this error message
"To continue using the LUIS portal, please migrate your apps to an Azure authoring resource"
There's a button there to start migration with this information
Azure Migration
Starting 12/01/2020, Language Understanding (LUIS) will require an Azure resource in an Azure subscription. In order to continue to have access to your LUIS apps, you need to migrate them to an Azure resource. This will walk you through the steps to migrate your apps to Azure.
Your key string will not be affected, therefore you can continue to use your authoring key normally to consume any LUIS API.
This is a live production instance so I don't want to cause any issues by continuing through these prompts.